REVIEW ARTICLE
Synthesis and function of ribosomal proteins – fading
models and new perspectives
Sara Caldarola, Maria Chiara De Stefano, Francesco Amaldi and Fabrizio Loreni
Department of Biology, University ‘Tor Vergata’, Roma, Italy
Introduction
Ribosomal proteins (RPs) are fundamental compo-
nents of ribosomes. They assemble with four rRNA
molecules in a complex process that takes place
sequentially in the nucleolus, in the nucleoplasm, and
in the cytoplasm. Nearly 200 nonribosomal factors are
required for the synthesis, maturation and export of
the two ribosomal subunits [1]. Most of the constitu-
ents of the preribosomal particles have been identified
in yeast by exploiting the potent combination of
genetic and biochemical approaches [2]. More recently,
advances in MS techniques have also led to the identi-
fication of the nucleolar proteome in human cells [3].
The role of RPs in the assembly of ribosomes has been
studied for many years. Reconstitution experiments in
prokaryotes have shown a specific order of addition of
RPs for self-assembly of ribosomal subunits [4,5]. The
greater complexity in the assembly of the eukaryotic
ribosome has until now prevented in vitro reconstitu-
tion. However, a recent analysis of the in vivo assembly
pathway of the 40S ribosomal subunit showed that the
formation of distinct structural intermediates may be
similar to what occurs in the prokaryotic counterpart
[6]. The structure and function of the ribosome appear
to be generally conserved in all organisms. The small
subunit (30S or 40S) contains the decoding center,

Surprisingly, the effect of the ribosomal stress is more dramatic in specific
physiological processes: hemopoiesis in humans, and pigmentation in mice.
Moreover, alteration of each RP impacts differently on the development of
an organism.
Abbreviations
Atg7, autophagy-related gene 7; CNBP, cellular nucleic acid-binding protein; DBA, Diamond–Blackfan anemia; E, embryonic day; eIF,
eukaryotic initiation factor; mTOR, mammalian target of rapamycin; NEDD8, neural-precursor-cell-expressed developmentally downregulated
8; PI3K, phosphoinositide-3-kinase; RP, ribosomal protein; S6K, S6 kinase; TOP, terminal oligopyrimidine; TSC, tuberous sclerosis complex;
TSS, transcription start site; USP10, ubiquitin-specific protease 10; ZNF9, zinc finger protein 9.
FEBS Journal 276 (2009) 3199–3210 ª 2009 The Authors Journal compilation ª 2009 FEBS 3199
and recycling phases of translation show differences
between prokaryotic and eukaryotic ribosomes [7].
Consistent with this observation, there are differences
in the protein composition of the ribosomes from the
different kingdoms. Of the 80 mammalian RPs, 49 are
related to archeal RPs, and 32 are homologous to bac-
terial proteins [8]. The remaining 11 RPs are specific
for eukaryotic ribosomes and may be involved in addi-
tional particular functions, such as intracellular trans-
port. Alternatively, they may be required for the more
complex regulation of eukaryotic protein synthesis [9].
The identification of the role of a specific RP is com-
plicated by the high level of cooperativity among ribo-
somal components and by the fact that the ribosome is
essential for the cell. Accordingly, most of the analyzed
eukaryotic RPs have been reported as being essential
for growth [9,10]. It can be postulated that RPs are
required for different steps of ribosome biogenesis
and ⁄ or ribosome function. Indeed, a systematic study
of the incorporation of RPs into preribosomes led to

biosynthesis of ribosomes to the requirements of cell
growth and differentiation. In addition, a relevant
contribution of protein turnover to the regulation of
RP synthesis and accumulation has been proposed by
recent studies [20]. Therefore, this review will focus on
the different aspects of translational and post-transla-
tional regulation of RP metabolism. We will also high-
light the role that studies on putative ribosome
pathologies have had in our understanding of regula-
tory mechanisms of RP synthesis.
Translational regulation of RP
synthesis
Sequence comparison of some vertebrate RP genes
cloned in the early 1980s revealed that these genes
share a characteristic and distinctive structure of the
transcription start site (TSS), which is always posi-
tioned within a pyrimidine stretch (about 10–25 nucle-
otides long), so that the transcribed mRNAs always
start with a C followed by a stretch of 5–15 pyrimi-
dines. Later, it was found that this TSS structure char-
acterizes all vertebrate RP genes, including all of the
80 human RP genes. This structure is rather peculiar,
given that the vast majority of mRNAs start with a
purine, most often an A. There are a number of other
genes, implicated directly or indirectly in translation,
that share this peculiar TSS structure. Among these,
we find all the translation elongation factors, but only
a few of the numerous translation initiation factors,
i.e. eukaryotic initiation factor (eIF) 3e, eIF3f, and
eIF3h [21].

region does not confer translational regulation on a
reporter mRNA without the TOP sequence, it does
contribute to the stringency of the regulation of a TOP
containing RP mRNA [23].
Putative trans-acting factor(s) that might be involved
in the growth-dependent translational regulation of RP
mRNAs have remained more elusive. In Xenopus , two
proteins have been identified, La and cellular nucleic
acid-binding protein (CNBP) ⁄ zinc finger protein 9
(ZNF9), which bind the 5¢-UTRs of RP mRNAs in vitro.
La interacts with the TOP sequence, whereas CNBP
binds a sequence element located closely downstream
[24,25]. The mutually exclusive binding of these two
proteins on the 5¢-UTRs of TOP mRNAs led
Pellizzoni to propose that La may increase translation,
whereas CNBP ⁄ ZNF9 could act as a translational
repressor. The interaction of La with RP mRNA has
also been confirmed in human cells, where La has been
shown to exist in two distinct states that differ in sub-
cellular localization [26]. When La is phosphorylated
on serine 366, it is localized in the nucleus, where it
has a role in polymerase III gene transcription. In con-
trast, nonphosphorylated La is found in the cytoplasm,
where it binds TOP mRNAs. Moreover, immunocom-
plex precipitation of La from HeLa cellular extracts
yields a number of mRNAs, including TOP mRNAs,
thus supporting the conclusion that La protein binds
TOP mRNAs in vivo. More recently, it has been shown
that La can also be phosphorylated by AKT, which is
a component of a signaling pathway involved in TOP

inconsistencies could be that additional factors contrib-
ute to the regulation. For instance, Ro60 is known to
interact with La and CNBP ⁄ ZNF9, whereas small
RNAs (Y) form a complex with La. If all of these
factors play a role in the regulation, the overexpression
or downregulation of only one of them could produce
apparently contradictory results in different experimen-
tal systems and conditions. A different situation is pre-
sented in a recent report by Orom et al. These authors
indicate microRNA-10a to be a trans-acting element
implicated in the translational regulation of RP
mRNAs [31]. The pairing of microRNA-10a with
the 5¢-UTRs of three RP mRNAs stimulates RP
mRNA translation. This mechanism is unusual for
microRNAs because, in general, they have a negative
effect on mRNA translation by interacting with their
3¢-UTRs [32], and it is not known whether it can be
extended to other TOP mRNAs.
Signaling pathways to RP mRNA
translation
As most of the reports addressing signaling consider
TOP mRNA as a homogeneous group, in this section
we will refer to RP mRNA as TOP mRNA. In the last
15 years, various research groups have studied the sig-
nal transduction pathways involved in TOP mRNA
translational control. Polysome separation on sucrose
gradients, which allows analysis of the polysome ⁄ sub-
polysome distribution of a messenger, has been used to
monitor the translation efficiency of TOP messengers
in different growth conditions. A variety of signals,

HeLa cells, it totally blocks the recruitment of TOP
messengers on polysomes during serum stimulation
[33]. In other cell lines, however, this inhibitory effect
is only partial [34,36]. Recent data from the Meyuhas
group indicate that mTOR is indispensable for the
translational activation of TOP mRNAs [37]. How-
ever, these authors showed that decreasing the expres-
sion of the raptor or rictor genes (partners of
mTORC1 and mTORC2 respectively) has only a slight
effect on the translation efficiency of TOP mRNAs.
This result implies that mTOR regulates TOP mRNA
translation through a novel rapamycin-insensitive
pathway with a minor, if any, contribution of the
canonical mTOR complexes mTORC1 and mTORC2.
A further downstream target of the PI3K pathway is
RPS6, which is phosphorylated after mitogenic stimu-
lation by two closely related kinases, S6 kinase (S6K)
1 and S6K2. The strong correlation between the trans-
lational activation of TOP mRNAs and the hyper-
phosphorylation of RPS6 [36] led to the assumption
that RPS6 phosphorylation was necessary for the
recruitment of TOP messengers to the polysomes [38].
For years, RPS6 has been considered to be the key
protein responsible for the selective translation of TOP
mRNAs able to increase the affinity of ribosomes
for this class of messengers. However, this model was
initially questioned by the observation that in cells
Ribosomal protein synthesis S. Caldarola et al.
3202 FEBS Journal 276 (2009) 3199–3210 ª 2009 The Authors Journal compilation ª 2009 FEBS
from S6K1

translation in eukaryotic cells. It is thought to enhance
the translation of mRNAs with highly structured
5¢-UTRs [42], and to play an important role in cell
growth and proliferation [43,44]. Moreover, eIF4E is
overexpressed in many kinds of cancer, and its abun-
dance is correlated with the progression of malignan-
cies [45]. In order to identify messengers regulated by
eIF4E, Sonenberg et al. performed a microarray analy-
sis of polysome-associated mRNAs from NIH3T3 cells
overexpressing eIF4E. They identified messengers cod-
ing for proteins involved in cell proliferation (MIF and
cenpA), survival (i.e. survivin, BI-1, and dad1), and
ribosome biogenesis (members of the small and large
ribosomal subunits). Interestingly, not all RP mRNAs
respond to eIF4E overexpression, suggesting the
existence of subclasses of TOP mRNAs with different
regulatory mechanisms.
RP turnover
Ribosome production is strongly linked to the rate of
cellular growth. The construction of ribosomes is
among the most energy-consuming events that occur in
a cell. A growing HeLa cell synthesizes about 7500
ribosomal subunits per minute, using up some 300 000
RPs, accounting for almost 50% of all cellular proteins
in growing cells [46]. Mature ribosomes are very stable
complexes, with an estimated half-life of about 5 days
for both RPs and rRNA [47]. Several laboratories have
tried to understand how ribosomes are recycled and
whether there is a specific mechanism of degradation to
adjust their number. In a recent report by the Andersen

cell cycle-regulated, and increases the translational effi-
ciency of ribosomes, indicating that addition of ubiqu-
itin molecules to RPs can also have a nonproteolytic
role (as previously shown for histones [52]). In addi-
tion, the molecular chaperone Hsp90 has been shown
to interact with RPS3 and RPS6, protecting them from
ubiquitination and proteasome-dependent degradation
[50]. Ubiquitination also has a role in ribosome biogen-
esis. In fact, it has been shown that proteasome inhibi-
tion alters both rRNA gene transcription and
maturation of the 90S preribosome complex; it also
leads to the depletion of 18S and 28S [51]. Moreover,
ubiquitin molecules on RPs can promote ribosome
assembly. In fact, in eukaryotes, RPL40, RPS27a and
RPP1 are synthesized as ubiquitin fusions, although the
ubiquitin part is then removed by post-translational
modification [53,54]. The transient association between
ubiquitin and RPs can promote their incorporation
into mature ribosomes, and is required for efficient
ribosome biogenesis. Another post-translational modifi-
cation of RPs has been shown by Hay et al., who, in
the search for novel proteins modified by neural-pre-
cursor-cell-expressed developmentally downregulated 8
(NEDD8) conjugation, identified 36 RPs from both
small and large subunits [55]. NEDD8 is a ubiquitin-
like molecule involved in the regulation of protein sta-
bility that can modulate cell proliferation and survival.
Its best characterized substrates are members of the
cullin family of proteins [56]. NEDDylation can have
opposite effects on the stability of its molecular targets:

somes (summarized in Fig. 1).
RPs in human pathologies and animal
models
Ribosome deficiencies due to mutations in the genes
coding for RPs or for rRNA have been known for
many years in Drosophila and Xenopus [59–61]. In both
cases, the main phenotype is slow growth, as expected
in the case of protein synthesis impairment. It was
quite surprising, therefore, that mutations were identi-
fied in the RPS19 gene as being the cause of Dia-
mond–Blackfan anemia (DBA) [62]. In fact, this
syndrome is characterized principally by defective
erythropoiesis associated with a variable degree of
growth retardation and malformations. Most RPS19
mutations are whole gene deletions, translocations, or
truncating mutations (nonsense or frameshift), suggest-
ing that haploinsufficiency is the basis of DBA patho-
logy. However, several missense mutations have also
been described [63]. The recent finding that mutations
in other RPs are also involved in DBA strongly sug-
gests that a ribosomal failure is responsible for the
clinical phenotype. Among DBA patients, mutations
have been found in RPS19 (25%), RPL5 (9%), RPL11
(6%), RPL35a (3%), RPS24 (2%), RPS17 (1%), and
RPS7 (< 1%) [62,64–67]. At present, these mutations
account for about 50% of DBA cases, and other
mutated RPs could therefore be found. Although an
additional tissue-specific role for the involved RPs
[68,69] cannot be ruled out, the most likely hypothesis
is that erythropoiesis is the human developmental pro-

such requirements would trigger apoptosis, possibly
through specific mechanisms (ribosomal stress). The
several animal models with RP deficiency reported in
the literature only partially support this hypothesis.
The first alteration of an RP in mice was an inducible
deletion of both copies of the RPS6 gene in the liver
of adult mice [77]. In this study, the altered response
to partial hepatectomy suggested the existence of a
novel checkpoint preventing cell cycle progression as a
consequence of a defect in ribosome biogenesis. Subse-
quently, the same research group showed that genetic
inactivation of p53 in RPS6-haploinsufficient mouse
embryos bypassed the observed blocking of the cell
cycle at gastrulation [embryonic day (E) 5.5]. The res-
cued embryos developed until E12.5, when they died
with diminished fetal liver erythropoiesis and placental
defects [78]. A less severe phenotype was observed in
the belly spot and tail mouse mutation, which is a
deletion in the RPL24 gene causing a splicing defect.
Belly spot and tail homozygotes die before E9.5, but
the heterozygotes reach adulthood, although they are
smaller than wild-type littermates [79]. More specific
phenotypes of Bst ⁄ + mice include alterations in pig-
mentation (white ventral midline spot, white hind feet),
skeletal abnormalities (kinked tail), and defects in reti-
nal development. An even less drastic phenotype is
observed in the case of mutations of the RPL29 gene.
In fact, mice lacking one of the two alleles develop
normally, and even RPL29-null animals are viable. A
delay in global growth is, however, observed in null

red cells, growth) are dependent on the increase in
p53. Hyperpigmentation is therefore due to stimulation
of the production of Kit ligand in keratinocytes, which
in turn causes melanocytosis. Another mouse knockout
model for RPS19 produced results partially in contrast
with this last report. In fact, the RPS19
) ⁄ )
animals die
prior to implantation, whereas heterozygous mice have
a normal phenotype, including the hematopoietic sys-
tem [83]. Finally, interesting new information has also
been obtained from zebrafish models. Amsterdam
et al. [84] reported that many RP genes may act as
tumor suppressors. Moreover, tumors due to RP hap-
loinsufficiency show defects in p53 synthesis, suggest-
ing that appropriate amounts of RPs are required for
p53 protein production in vivo, and that disruption of
this regulation could contribute to tumorigenesis [85].
In other studies, RP deficiency was induced by inject-
ing antisense oligonucleotide analogs (morpholinos)
into one-cell-stage zebrafish embryos. The reduced
amounts of RPS19 and several other RPs caused
hematopoietic and developmental abnormalities similar
to DBA [86,87]. Interestingly RPL11-deficient embryos
display abnormalities mostly in the brain [88]. Simi-
larly to some mouse models, RP deficiency in zebrafish
seems to activate a p53-dependent checkpoint that
induces developmental abnormalities [86,88]. The
affected tissues, however, could be different according
to the RP involved. Vertebrate animal models for RP

New studies on RP turnover have opened up a
scenario of additional regulatory mechanisms in RP
Table 1. Vertebrate animal models with RP alterations.
RP Organism Alteration Phenotype p53 inhibition References
RPS6 Mouse Conditional deletion (liver) Cell cycle block Not done [77]
RPS6 Mouse Deletion ) ⁄ +: embryonic lethal Partial rescue [78]
RPS19 Mouse Deletion ) ⁄ +: no phenotype
) ⁄ ): lethal
Not done [83]
RPS19 Zebrafish Knock-down Hematopoietic and developmental
abnormalities
Rescue [86,87]
RPS19, RPS20 Mouse Missense mutations
(Dsk3 and Dsk4)
Dsk ⁄ +: alteration of pigmentation,
erythrocyte development
Dsk ⁄ Dsk: lethal
Rescue [82]
RPL11 Zebrafish Knock-down Brain abnormalities, lethal Rescue [88]
RPL22 Mouse Deletion ) ⁄ +: no phenotype
) ⁄ ): viable, defect in alpha–beta
T-cells
Rescue [81]
RPL24 Mouse Missense mutation (Bst) Bst ⁄ +: alteration of pigmentation,
skeleton and retinal development
Bst ⁄ Bst: lethal
Not done [79]
RPL29 Mouse Deletion ) ⁄ +: no phenotype
) ⁄ ): viable, mild growth retardation
Not done [80]

is not entirely convincing. A more intriguing interpreta-
tion is a possible specific functional role of the various
RPs within the ribosome, as recently observed in yeast
[90]. As a consequence, RPs could be more or less
important for ribosome functioning, consistent with the
variable impact of mutations in different RPs observed
in mice (e.g. RPS6 > RPS19 > RPL22 > RPL29; see
also Table 1). A further extension of this hypothesis
could be heterogeneity in the composition of the ribo-
some, as shown in Ascaris [91], although there is no evi-
dence for this in vertebrates. Another possibility that
could partially explain the different impacts of muta-
tions in diverse RPs is a variable basal level (of both
mRNA and ⁄ or protein) in different tissues and ⁄ or
species. Despite some evidence for variability in the
amounts of RPs in different tissues, this aspect has not
yet been thoroughly analyzed. A final remark is that the
identification of human pathologies dependent on RP
mutations has stimulated interest in this group of basic
cell components. This has already helped to step up
research in this field, and will hopefully clarify issues
that remain unsolved.
Acknowledgements
We thank V. Iadevaia for the artwork. The financial
support of Telethon–Italy (Grant no. GGP07241A to
F. Loreni) is gratefully acknowledged. This work was
also supported by the Diamond Blackfan Anemia
Foundation, Inc. and the Italian Ministry of Univer-
sity and Research (FIRB and PRIN grants).
References

Milkereit P (2005) Roles of eukaryotic ribosomal pro-
teins in maturation and transport of pre-18S rRNA and
ribosome function. Mol Cell 20, 263–275.
11 Valasek L, Mathew AA, Shin BS, Nielsen KH, Szamecz
B & Hinnebusch AG (2003) The yeast eIF3 subunits
TIF32 ⁄ a, NIP1 ⁄ c, and eIF5 make critical connections
with the 40S ribosome in vivo. Genes Dev 17, 786–799.
12 Gasch AP, Spellman PT, Kao CM, Carmel-Harel O,
Eisen MB, Storz G, Botstein D & Brown PO (2000)
Genomic expression programs in the response of yeast
cells to environmental changes. Mol Biol Cell 11,
4241–4257.
13 Lieb JD, Liu X, Botstein D & Brown PO (2001) Pro-
moter-specific binding of Rap1 revealed by genome-
wide maps of protein–DNA association. Nat Genet 28,
327–334.
14 Hu H & Li X (2007) Transcriptional regulation in
eukaryotic ribosomal protein genes. Genomics 90,
421–423.
15 Hariharan N, Kelley DE & Perry RP (1989) Equipotent
mouse ribosomal protein promoters have a similar
architecture that includes internal sequence elements.
Genes Dev 3, 1789–1800.
S. Caldarola et al. Ribosomal protein synthesis
FEBS Journal 276 (2009) 3199–3210 ª 2009 The Authors Journal compilation ª 2009 FEBS 3207
16 Ishii K, Washio T, Uechi T, Yoshihama M, Kenmochi
N & Tomita M (2006) Characteristics and clustering of
human ribosomal protein genes. BMC Genomics 7, 37,
doi:10.1186/1471-2164-7-37.
17 Perry RP (2005) The architecture of mammalian

Effect of 3¢UTR length on the translational regulation
of 5¢-terminal oligopyrimidine mRNAs. Gene 344,
213–220.
24 Pellizzoni L, Cardinali B, Lin-Marq N, Mercanti D &
Pierandrei-Amaldi P (1996) A Xenopus laevis homo-
logue of the La autoantigen binds the pyrimidine tract
of the 5¢UTR of ribosomal protein mRNAs in vitro:
implication of a protein factor in complex formation.
J Mol Biol 259, 904–915.
25 Pellizzoni L, Lotti F, Maras B & Pierandrei-Amaldi P
(1997) Cellular nucleic acid binding protein binds a con-
served region of the 5¢ UTR of Xenopus laevis ribo-
somal protein mRNAs. J Mol Biol 267, 264–275.
26 Schwartz EI, Intine RV & Maraia RJ (2004) CK2 is
responsible for phosphorylation of human La protein
serine-366 and can modulate rpL37 5¢-terminal oligo-
pyrimidine mRNA metabolism. Mol Cell Biol 24, 9580–
9591.
27 Brenet F, Socci ND, Sonenberg N & Holland EC
(2009) Akt phosphorylation of La regulates specific
mRNA translation in glial progenitors. Oncogene 28,
128–139.
28 Crosio C, Boyl PP, Loreni F, Pierandrei-Amaldi P &
Amaldi F (2000) La protein has a positive effect on the
translation of TOP mRNAs in vivo. Nucleic Acids Res
28, 2927–2934.
29 Meerovitch K, Pelletier J & Sonenberg N (1989) A
cellular protein that binds to the 5¢-noncoding region of
poliovirus RNA: implications for internal translation
initiation. Genes Dev 3, 1026–1034.

the ‘polypyrimidine tract’ mRNA family. Proc Natl
Acad Sci USA 91, 4441–4445.
37 Patursky-Polischuk I, Stolovich-Rain M, Hausner-Han-
ochi M, Kasir J, Cybulski N, Avruch J, Ruegg MA,
Hall MN & Meyuhas O (2009) The TSC–mTOR path-
way mediates translational activation of TOP mRNAs
by insulin largely in a raptor- or rictor-independent
manner. Mol Cell Biol 29, 640–649.
38 Jefferies HBJ, Fumagalli S, Dennis PB, Reinhard C,
Pearson RB & Thomas G (1997) Rapamycin suppresses
5¢TOP mRNA translation through inhibition of p70s6k.
EMBO J 16, 3693–3704.
39 Pende M, Um SH, Mieulet V, Sticker M, Goss VL,
Mestan J, Mueller M, Fumagalli S, Kozma SC & Thomas
G (2004) S6K1() ⁄ )) ⁄ S6K2() ⁄ )) mice exhibit perinatal
lethality and rapamycin-sensitive 5¢-terminal oligopyrim-
idine mRNA translation and reveal a mitogen-activated
protein kinase-dependent S6 kinase pathway. Mol Cell
Biol 24, 3112–3124.
Ribosomal protein synthesis S. Caldarola et al.
3208 FEBS Journal 276 (2009) 3199–3210 ª 2009 The Authors Journal compilation ª 2009 FEBS
40 Ruvinsky I, Sharon N, Lerer T, Cohen H, Stolovich-Rain
M, Nir T, Dor Y, Zisman P & Meyuhas O (2005)
Ribosomal protein S6 phosphorylation is a determinant
of cell size and glucose homeostasis. Genes Dev 19,
2199–2211.
41 Mamane Y, Petroulakis E, Martineau Y, Sato TA, Lars-
son O, Rajasekhar VK & Sonenberg N (2007) Epigenetic
activation of a subset of mRNAs by eIF4E explains its
effects on cell proliferation. PLoS ONE 2 , e242,

49 Spence J, Gali RR, Dittmar G, Sherman F, Karin M &
Finley D (2000) Cell cycle-regulated modification of the
ribosome by a variant multiubiquitin chain. Cell 102,
67–76.
50 Kim TS, Jang CY, Kim HD, Lee JY, Ahn BY & Kim J
(2006) Interaction of Hsp90 with ribosomal proteins
protects from ubiquitination and proteasome-dependent
degradation. Mol Biol Cell 17, 824–833.
51 Stavreva DA, Kawasaki M, Dundr M, Koberna K,
Muller WG, Tsujimura-Takahashi T, Komatsu W,
Hayano T, Isobe T, Raska I et al. (2006) Potential roles
for ubiquitin and the proteasome during ribosome bio-
genesis. Mol Cell Biol 26, 5131–5145.
52 Robzyk K, Recht J & Osley MA (2000) Rad6-depen-
dent ubiquitination of histone H2B in yeast. Science
287, 501–504.
53 Archibald JM, Teh EM & Keeling PJ (2003) Novel
ubiquitin fusion proteins: ribosomal protein P1 and
actin. J Mol Biol 328, 771–778.
54 Kirschner LS & Stratakis CA (2000) Structure of the
human ubiquitin fusion gene Uba80 (RPS27a) and one
of its pseudogenes. Biochem Biophys Res Commun 270,
1106–1110.
55 Xirodimas DP, Sundqvist A, Nakamura A, Shen L, Bot-
ting C & Hay RT (2008) Ribosomal proteins are targets
for the NEDD8 pathway. EMBO Rep 9, 280–286.
56 Pan ZQ, Kentsis A, Dias DC, Yamoah K & Wu K
(2004) Nedd8 on cullin: building an expressway to pro-
tein destruction. Oncogene 23
, 1985–1997.

(RPS17) is mutated in Diamond–Blackfan anemia. Hum
Mutat 28, 1178–1182.
65 Farrar JE, Nater M, Caywood E, McDevitt MA,
Kowalski J, Takemoto CM, Talbot CC Jr, Meltzer P,
Esposito D et al. (2008) Abnormalities of the large ribo-
somal subunit protein, Rpl35a, in Diamond–Blackfan
anemia. Blood 112, 1582–1592.
66 Gazda HT, Grabowska A, Merida-Long LB, Latawiec
E, Schneider HE, Lipton JM, Vlachos A, Atsidaftos E,
Ball SE, Orfali KA et al. (2006) Ribosomal protein S24
gene is mutated in Diamond–Blackfan anemia. Am J
Hum Genet 79, 1110–1118.
S. Caldarola et al. Ribosomal protein synthesis
FEBS Journal 276 (2009) 3199–3210 ª 2009 The Authors Journal compilation ª 2009 FEBS 3209
67 Gazda HT, Sheen MR, Vlachos A, Choesmel V,
O’Donohue MF, Schneider H, Darras N, Hasman C,
Sieff CA, Newburger PE et al. (2008) Ribosomal
protein L5 and L11 mutations are associated with cleft
palate and abnormal thumbs in Diamond–Blackfan
anemia patients. Am J Hum Genet 83, 769–780.
68 Naora H (1999) Involvement of ribosomal proteins in
regulating cell growth and apoptosis: translational mod-
ulation or recruitment for extraribosomal activity?
Immunol Cell Biol 77, 197–205.
69 Wool IG (1996) Extraribosomal functions of ribosomal
proteins. Trends Biochem Sci 21, 164–165.
70 Ebert BL, Pretz J, Bosco J, Chang CY, Tamayo P,
Galili N, Raza A, Root DE, Attar E, Ellis SR et al.
(2008) Identification of RPS14 as a 5q- syndrome
gene by RNA interference screen. Nature 451,

Thomas G (2000) Proliferation, but not growth,
blocked by conditional deletion of 40S ribosomal
protein S6. Science 288, 2045–2047.
78 Panic L, Tamarut S, Sticker-Jantscheff M, Barkic M,
Solter D, Uzelac M, Grabusic K & Volarevic S
(2006) Ribosomal protein S6 gene haploinsufficiency
is associated with activation of a p53-dependent
checkpoint during gastrulation. Mol Cell Biol 26,
8880–8891.
79 Oliver ER, Saunders TL, Tarle SA & Glaser T (2004)
Ribosomal protein L24 defect in belly spot and tail
(Bst), a mouse Minute. Development 131, 3907–3920.
80 Kirn-Safran CB, Oristian DS, Focht RJ, Parker SG,
Vivian JL & Carson DD (2007) Global growth deficien-
cies in mice lacking the ribosomal protein HIP ⁄ RPL29.
Dev Dyn 236, 447–460.
81 Anderson SJ, Lauritsen JP, Hartman MG, Foushee
AM, Lefebvre JM, Shinton SA, Gerhardt B, Hardy
RR, Oravecz T & Wiest DL (2007) Ablation of ribo-
somal protein L22 selectively impairs alphabeta T cell
development by activation of a p53-dependent check-
point. Immunity 26, 759–772.
82 McGowan KA, Li JZ, Park CY, Beaudry V, Tabor
HK, Sabnis AJ, Zhang W, Fuchs H, de Angelis MH,
Myers RM et al. (2008) Ribosomal mutations cause
p53-mediated dark skin and pleiotropic effects. Nat
Genet 40
, 963–970.
83 Matsson H, Davey EJ, Draptchinskaia N, Hamaguchi
I, Ooka A, Leveen P, Forsberg E, Karlsson S & Dahl

Functional specificity among ribosomal proteins regu-
lates gene expression. Cell 131, 557–571.
91 Etter A, Bernard V, Kenzelmann M, Tobler H & Muller
F (1994) Ribosomal heterogeneity from chromatin dimi-
nution in Ascaris lumbricoides. Science 265, 954–956.
Ribosomal protein synthesis S. Caldarola et al.
3210 FEBS Journal 276 (2009) 3199–3210 ª 2009 The Authors Journal compilation ª 2009 FEBS