Sequences coding for the ribosomal protein L14 in Xenopus laevis and Xenopus tropicalis; homologies in the 5' untranslated region are shared with other r-protein mRNAs

The cloning and sequencing of a ribosomal L18 protein from an evolutionary divergent eukaryote, Trypanosoma brucei

Eukaryotic ribosomal proteins are highly conserved across widely divergent species, suggesting that strong functional constraints prevent divergence of important amino acid motifs. Using this as a basis, an evolutionary approach could be used to identify putative functional motifs. We obtained the DNA sequence of the ribosomal protein L18 from the evolutionary divergent protozoan parasite, Trypanosoma brucei. Analysis of this sequence showed that it had 46% and 43% identity with the human and yeast sequences, respectively, and 30% of amino acid residues were identical across all the species analysed. Using these data, amino acids essential to the structure and function of ribosomal protein L18 can be inferred and could provide valuable information for molecular modelling and mutational studies.

Cloning, expression, and localization of a new member of a Paracentrotus lividus cell surface multigene family

We have isolated and characterized a cDNA clone corresponding to a new member of bep (butanol, extracted, proteins) Paracentrotus lividus multigene family coding for cell surface proteins. The cDNA, called bep3, encodes a 370 amino acid protein and shares the same structural organization in the coding region with other members of the same gene family already characterized. Expression of this clone studied by Northern blot and by whole mount hybridization shows that the bep3 messenger is transcribed during oogenesis and utilized till the gastrula stage, whereas at the prism stage, unlike other members of the same gene family, new synthesis of messenger occurs. By whole mount hybridization spatial distribution of bep3 messenger in egg and embryos is established. This messenger appears located in the animal half of the unfertilized egg and moves to the cortical zone after fertilization; it is not present in the structures derived by the vegetal part of the embryo, such as the micromeres of the 16-cell stage, the primary mesenchyme cells of the blastula, and the primary intestine of the gastrula. At the prism stage instead, hybridization of bep3 messenger is restricted to the part of the embryo that will give origin to the oral region as successively confirmed by hybridization at the pluteus stage. The result of whole mount hybridization was confirmed by Northern blot hybridization of separated meso-macromere and micromere RNAs. A Southern blot experiment demonstrates that bep3 is codified by a single copy gene. Conservation of the bep multigene family in several Mediterranean and Japanese sea urchin species has also been analyzed.

Structure and expression of ribosomal protein genes in Xenopus laevis

In Xenopus laevis, as well as in other vertebrates, ribosomal proteins (r-proteins) are coded by a class of genes that share some organizational and structural features. One of these, also common to genes coding for other proteins involved in the translation apparatus synthesis and function, is the presence within their introns of sequences coding for small nucleolar RNAs. Another feature is the presence of common structures, mainly in the regions surrounding the 5' ends, involved in their coregulated expression. This is attained at various regulatory levels: transcriptional, posttranscriptional, and translational. Particular attention is given here to regulation at the translational level, which has been studied during Xenopus oogenesis and embryogenesis and also during nutritional changes of Xenopus cultured cells. This regulation, which responds to the cellular need for new ribosomes, operates by changing the fraction of rp-mRNA (ribosomal protein mRNA) engaged on polysomes. A typical 5' untranslated region characterizing all vertebrate rp-mRNAs analyzed to date is responsible for this translational behaviour: it is always short and starts with an 8-12 nucleotide polypyrimidine tract. This region binds in vitro some proteins that can represent putative trans-acting factors for this translational regulation.

A cDNA encoding Arabidopsis thaliana cytoplasmic ribosomal protein L18

A cDNA encoding ribosomal (r) protein L18 of Arabidopsis thaliana (At) was isolated and characterized. The nucleotide sequence contains a 563-bp open reading frame that encodes a 20.9-kDa basic protein. Amino-acid comparison indicated that the predicted L18 r-protein of At has a high degree of homology with L18 of distantly related organisms such as yeast, Xenopus laevis and rat. Genomic DNA analysis suggested that L18 is encoded by a single locus in At. An mRNA of approx. 0.9 kb is detected in all the tissues and developmental stages analyzed.

Identification and characterization of a cDNA encoding ribosomal protein S12 from Xenopus laevis

The complete nucleotide (nt) sequence of the cDNA clone XL-S12, encoding a Xenopus laevis (Xl) homologue of the mammalian ribosomal protein S12, has been determined. The sequence predicts a Xl S12 protein of 132 amino acids (aa) with a molecular mass of 14.7 kDa. Xl S12 shares 95 and 97% aa sequence identity with the human and murine S12 proteins, respectively. Analysis of nt substitution patterns and rates indicates that S12 is a very highly constrained protein, evolving at an estimated rate of only 0.03 x 10(-9) non-synonymous (protein-altering) substitutions per site per year.

Vertebrate mRNAs with a 5'-terminal pyrimidine tract are candidates for translational repression in quiescent cells: characterization of the translational cis-regulatory element

The translation of mammalian ribosomal protein (rp) mRNAs is selectively repressed in nongrowing cells. This response is mediated through a regulatory element residing in the 5' untranslated region of these mRNAs and includes a 5' terminal oligopyrimidine tract (5' TOP). To further characterize the translational cis-regulatory element, we monitored the translational behavior of various endogenous and heterologous mRNAs or hybrid transcripts derived from transfected chimeric genes. The translational efficiency of these mRNAs was assessed in cells that either were growing normally or were growth arrested under various physiological conditions. Our experiments have yielded the following results: (i) the translation of mammalian rp mRNAs is properly regulated in amphibian cells, and likewise, amphibian rp mRNA is regulated in mammalian cells, indicating that all of the elements required for translation control of rp mRNAs are conserved among vertebrate classes; (ii) selective translational control is not confined to rp mRNAs, as mRNAs encoding the naturally occurring ubiquitin-rp fusion protein and elongation factor 1 alpha, which contain a 5' TOP, also conform this mode of regulation; (iii) rat rpP2 mRNA contains only five pyrimidines in its 5' TOP, yet this mRNA is translationally controlled in the same fashion as other rp mRNAs with a 5' TOP of eight or more pyrimidines; (iv) full manifestation of this mode of regulation seems to require both the 5' TOP and sequences immediately downstream; and (v) an intact translational regulatory element from rpL32 mRNA fails to exert its regulatory properties even when preceded by a single A residue.

Aspects of regulation of ribosomal protein synthesis in Xenopus laevis. Review

The work carried out in the authors' laboratories on the structure and expression of ribosomal protein genes in Xenopus is reviewed, with some comparisons with other systems. These genes form a class that shares several structural features, especially in the region surrounding the 5' ends. These similar structures appear to be involved in coregulated expression that is attained at various regulatory levels: transcriptional, transcript processing and stability, and translational. Particular attention is paid here to the one operating at the translational level, which has been studied during Xenopus oogenesis and embryogenesis, and also during nutritional changes of Xenopus cultured cells. This regulation, which responds to the cellular need for new ribosomes, operates by changing the fraction of rp-mRNA engaged on polysomes, leaving each translated rp-mRNA molecule always fully loaded with ribosomes. Responsible for this translational behaviour is the typical 5'UTR, which characterizes all rp-mRNAs analyzed up to now, and that can bind in vitro some proteins, putative trans-acting factors for this translational regulation.

Vertebrate mRNAs with a 5'-terminal pyrimidine tract are candidates for translational repression in quiescent cells: characterization of the translational cis-regulatory element

The translation of mammalian ribosomal protein (rp) mRNAs is selectively repressed in nongrowing cells. This response is mediated through a regulatory element residing in the 5' untranslated region of these mRNAs and includes a 5' terminal oligopyrimidine tract (5' TOP). To further characterize the translational cis-regulatory element, we monitored the translational behavior of various endogenous and heterologous mRNAs or hybrid transcripts derived from transfected chimeric genes. The translational efficiency of these mRNAs was assessed in cells that either were growing normally or were growth arrested under various physiological conditions. Our experiments have yielded the following results: (i) the translation of mammalian rp mRNAs is properly regulated in amphibian cells, and likewise, amphibian rp mRNA is regulated in mammalian cells, indicating that all of the elements required for translation control of rp mRNAs are conserved among vertebrate classes; (ii) selective translational control is not confined to rp mRNAs, as mRNAs encoding the naturally occurring ubiquitin-rp fusion protein and elongation factor 1 alpha, which contain a 5' TOP, also conform this mode of regulation; (iii) rat rpP2 mRNA contains only five pyrimidines in its 5' TOP, yet this mRNA is translationally controlled in the same fashion as other rp mRNAs with a 5' TOP of eight or more pyrimidines; (iv) full manifestation of this mode of regulation seems to require both the 5' TOP and sequences immediately downstream; and (v) an intact translational regulatory element from rpL32 mRNA fails to exert its regulatory properties even when preceded by a single A residue.

Molecular characterization of the mouse ribosomal protein S24 multigene family: a uniquely expressed intron-containing gene with cell-specific expression of three alternatively spliced mRNAs

A family of 16 genes encoding the mouse ribosomal protein S24 was identified, and four members from this family were cloned. A single expressed intron-containing S24 gene (termed mrpS24) and one pseudogene (mrpS24p) were completely sequenced and characterized. The mrpS24 gene has seven exons and six introns spanning over 5.1 x 10(3) nucleotides (nt). The cap site of S24 was mapped to a G residue four nt upstream of a polypyrimidine tract and 15 nt downstream of a TATA-like (TATGA) element. The 5' region (-325 to +33) of the mrpS24 gene has a functional promoter that was able to express the fused chloramphenicol acetyltransferase (CAT) reporter gene. Two different forms of mouse S24 cDNA clones were previously isolated. Sequence analysis showed that one of these cDNA clones (termed S24a) lacks the entire exon V sequence (18 nt), and the deduced amino acid sequence is missing a C-terminal lysine residue encoded by the other cDNA (S24b). The pseudogene mrpS24p is flanked by an 11-bp direct repeat, and its sequence is almost identical to the S24 cDNA sequence, but it lacks two mini-exons, V and VI (20 nt), as in the cases of the human and rat S24 cDNAs. RT-PCR experiments demonstrated the existence of a third form (S24c) that similarly lacks both of the mini-exons, and suggested that different species of S24 mRNA might arise from alternative splicing of the mini-exons V and VI. Northern blot analysis showed that S24 expression is down- and up-regulated during adipocyte differentiation and in cellular transformation, respectively. RNase protection assays and RT-PCR experiments suggested that these cell-specific changes of S24 mRNA levels are mainly due to fluctuations in S24c mRNA level. Our results provide the first indication that a ribosomal protein gene is regulated by alternative usage of two mini-exons in a cell-specific manner.

XrpFI, an amphibian transcription factor composed of multiple polypeptides immunologically related to the GA-binding protein alpha and beta subunits, is differentially expressed during Xenopus laevis development

XrpFI, first identified in the extract of Xenopus laevis oocyte nuclei, binds to a proximal sequence of the L14 ribosomal protein gene promoter. Its target sequence, 5'-TAACCGGAAGTTTGT-3', is required to fully activate the promoter, and the two G's of the central motif are essential for factor binding and transcriptional activation; our data also suggest that XrpFI may play a role in cap site positioning. The binding site of XrpFI is homologous to the sequence recognized by the family of ets genes. Antibodies specific for Ets-1 and Ets-2 proteins did not react with XrpFI, but those raised against the rat alpha and beta GA-binding proteins both supershifted the retarded bands formed by XrpFI. The Xenopus polypeptides related to GA-binding protein alpha interact with DNA both as monomers and as heterodimers associated with beta-related proteins. Oocyte nuclei contain multiple forms of alpha- and beta-related proteins: the alpha-like proteins remain throughout development, while the pattern of the beta species changes in the embryonic stages examined. beta-like proteins are undetectable in the cleavage period up to the neurula stage, but at later stages, when ribosomal protein genes are actively transcribed, two beta-related polypeptides reappear.

Nucleotide and deduced amino acid sequence of human ribosomal protein L18

Ribosomal protein L18 mRNA is overexpressed in human colorectal cancer compared to normal colon tissue. We report the nucleotide sequence of human L18 cDNA derived from a normal colon source. There were no mutational changes in segments of L18 cDNA derived from two tumor sources. The L18 cDNA was 690 base pairs long and predicts a single open reading frame of 564 nucleotides, encoding 188 amino acids with a M(r) = 21,621, it is homologous to rat L18 and Xenopus laevis L14.

XrpFI, an amphibian transcription factor composed of multiple polypeptides immunologically related to the GA-binding protein alpha and beta subunits, is differentially expressed during Xenopus laevis development

XrpFI, first identified in the extract of Xenopus laevis oocyte nuclei, binds to a proximal sequence of the L14 ribosomal protein gene promoter. Its target sequence, 5'-TAACCGGAAGTTTGT-3', is required to fully activate the promoter, and the two G's of the central motif are essential for factor binding and transcriptional activation; our data also suggest that XrpFI may play a role in cap site positioning. The binding site of XrpFI is homologous to the sequence recognized by the family of ets genes. Antibodies specific for Ets-1 and Ets-2 proteins did not react with XrpFI, but those raised against the rat alpha and beta GA-binding proteins both supershifted the retarded bands formed by XrpFI. The Xenopus polypeptides related to GA-binding protein alpha interact with DNA both as monomers and as heterodimers associated with beta-related proteins. Oocyte nuclei contain multiple forms of alpha- and beta-related proteins: the alpha-like proteins remain throughout development, while the pattern of the beta species changes in the embryonic stages examined. beta-like proteins are undetectable in the cleavage period up to the neurula stage, but at later stages, when ribosomal protein genes are actively transcribed, two beta-related polypeptides reappear.

Functional elements of the ribosomal protein L7a (rpL7a) gene promoter region and their conservation between mammals and birds

The transcriptional initiation sites of the chicken ribosomal protein L7a (rpL7a) gene have been determined and found to occur at three consecutive cytidine residues at the start of a polypyrimidine tract of 8 base pairs (bp). A comparative analysis of the 5' upstream regions of the mouse, human and chicken rpL7a genes identified two sequence elements (Box A and Box B) conserved over the 600 million years of divergent evolution that separate mammals and birds. Only Box A (nts - 56 to - 39) and Box B (nts - 25 to - 4) sequences were detected to bind nuclear factors from mouse nuclear extracts in an analysis of the mouse rpL7a 5' upstream sequence. Box A and Box B bind different nuclear factors and the factor binding to mouse Box A and mouse Box B sequences could be effectively competed by corresponding homologous sequences from the human and chicken rpL7a promoters. These results indicate that elements of the rpL7a promoter region are conserved between mammals and birds. An in vivo analysis of the mouse rpL7a 5' upstream sequence required for efficient transcription identified the 5' border of the minimal promoter region as lying between nts - 50 and - 56. Constructs containing 56 bp of 5' upstream DNA and the first 25 bp rpL7a exon were very efficiently transcribed indicating that sequences within the first intron are not required for gene expression. No sequence similarity was detected between the rpL7a promoter elements and described promoter elements of other eukaryotic ribosomal protein genes.

Individual variability in the translational regulation of ribosomal protein synthesis in Xenopus laevis

Ribosomal protein synthesis is regulated by controlling the fraction of mRNA associated with polysomes. It is known that this value changes in different developmental stages during Xenopus embryogenesis or, more generally, with changing cell growth conditions. We present here an analysis of the proportion of mRNA loaded on polysomes, carried out with probes for five different ribosomal proteins on several batches of Xenopus embryos obtained from different individuals. The results obtained indicate the existence of probe-dependent and individual differences, which reflect genetic variations in the cis- and trans-acting regulatory elements responsible for translational regulation. The fraction of ribosomal protein mRNA loaded onto polysomes can be used as an index of an individual's capacity for ribosome production.

Analysis of mRNAs under translational control during Xenopus embryogenesis: isolation of new ribosomal protein clones

We have analyzed several randomly selected mRNAs, of the relatively abundant category, on the basis of maternal or zygotic origin and translational efficiency at different developmental stages. For this purpose, clones from a Xenopus embryo cDNA library were hybridized with cDNA probes prepared with poly(A)+RNA from polysomes and from mRNPs of embryos at different stages. The results obtained indicate that the majority of the relatively abundant mRNAs (38 out of 61) is subject to some kind of translational regulation during embryogenesis. Moreover, 30 clones have been selected as corresponding to mRNAs that behave, from the point of view of transcriptional and translational regulation, similarly to previously studied ribosomal protein (r-protein) mRNAs. Sequence analysis of 20 of these selected cDNAs has shown that half of them are in fact homologous to already sequenced r-protein mRNAs. Unexpectedly we have found that also the mRNA for alpha-cardiac actin and another mRNA homologous to creatine kinase M mRNA have a similar translational regulation during embryogenesis.

Sequence of a cDNA clone encoding an Atlantic salmon ribosomal protein

We report here the nucleotide sequence of a cDNA clone encoding a salmon (Salmo salar) ribosomal (r) protein. The encoded protein shows 62.3% and 62% similarity with the L14 and L18 r-proteins in Xenopus laevis and rat, respectively.

HrpF, a human sequence-specific DNA-binding protein homologous to XrpFI, a Xenopus laevis oocyte transcription factor

The identification in HeLa nuclei of a novel DNA-binding protein, designated HrpF, is presented. This factor recognizes and binds a sequence of the Xenopus laevis L14 ribosomal protein (r-p) gene promoter bound by the Xenopus r-p transcription factor I (XrpFI). We show here that XrpFI and HrpF share a conserved DNA-binding domain. We also present evidences suggesting that the two factors perform similar functions in the cell. We discuss the hypothesis that closely related factors might be involved in the control of rp-gene transcription in vertebrates.

Two evolutionarily divergent genes encode a cytoplasmic ribosomal protein of Arabidopsis thaliana

Two clones of Arabidopsis thaliana possessing high sequence identity to the yeast gene encoding ribosomal (r) protein L3 were isolated by heterologous DNA hybridization. The coding regions of these two clones have approx. 63% amino acid (aa) sequence identity to the yeast L3 r-protein and 85% aa sequence identity to each other. Both genes are expressed in shoots. The presence of two divergent genes in A. thaliana raises the possibility that the gene products participate in the formation of functionally distinct ribosomes.

Structure of Xenopus laevis ribosomal protein L32 and its expression during development

cDNA clones for Xenopus laevis ribosomal protein L32 have been isolated and sequenced. The deduced amino acid sequence indicates that L32 is a basic protein of 110 amino acids, has a molecular weight of 12,603 and is homologous to the rat ribosomal protein L35. Using the cDNA clone as a probe to follow the expression of this gene during Xenopus development, it has been shown that the pattern of accumulation of this mRNA follows the one previously described for other ribosomal protein mRNAs during oogenesis and embryogenesis. The analysis of the utilization of L32 mRNA during embryogenesis shows that this is controlled by the translational regulation typical of other ribosomal protein mRNAs.

The 5' untranslated region of mRNA for ribosomal protein S19 is involved in its translational regulation during Xenopus development

During Xenopus development, the synthesis of ribosomal proteins is regulated at the translational level. To identify the region of the ribosomal protein mRNAs responsible for their typical translational behavior, we constructed a fused gene in which the upstream sequences (promoter) and the 5' untranslated sequence (first exon) of the gene coding for Xenopus ribosomal protein S19 were joined to the coding portion of the procaryotic chloramphenicol acetyltransferase (CAT) gene deleted of its own 5' untranslated region. This fused gene was introduced in vivo by microinjection into Xenopus fertilized eggs, and its activity was monitored during embryogenesis. By analyzing the pattern of appearance of CAT activity and the distribution of the S19-CAT mRNA between polysomes and messenger ribonucleoproteins, it was concluded that the 35-nucleotide-long 5' untranslated region of the S19 mRNA is able to confer to the fused S19-CAT mRNA the translational behavior typical of ribosomal proteins during Xenopus embryo development.

The 5' untranslated region of mRNA for ribosomal protein S19 is involved in its translational regulation during Xenopus development

During Xenopus development, the synthesis of ribosomal proteins is regulated at the translational level. To identify the region of the ribosomal protein mRNAs responsible for their typical translational behavior, we constructed a fused gene in which the upstream sequences (promoter) and the 5' untranslated sequence (first exon) of the gene coding for Xenopus ribosomal protein S19 were joined to the coding portion of the procaryotic chloramphenicol acetyltransferase (CAT) gene deleted of its own 5' untranslated region. This fused gene was introduced in vivo by microinjection into Xenopus fertilized eggs, and its activity was monitored during embryogenesis. By analyzing the pattern of appearance of CAT activity and the distribution of the S19-CAT mRNA between polysomes and messenger ribonucleoproteins, it was concluded that the 35-nucleotide-long 5' untranslated region of the S19 mRNA is able to confer to the fused S19-CAT mRNA the translational behavior typical of ribosomal proteins during Xenopus embryo development.

Nuclear factors specifically bind to upstream sequences of a Xenopus laevis ribosomal protein gene promoter

The upstream region of the Xenopus laevis L14 ribosomal protein gene was deleted starting from the 5' extremity in order to define the promoter length necessary to express a linked reporter CAT gene. The functional analysis indicated that a sequence located between -63 and -49 from the capsite is important for an efficient promoter activity. Band shift and ExoIII protection assays evidenced the binding to this region of a factor, called XrpFI, present in the crude nuclear extract from X.laevis oocytes. Methylation interference analysis localized the contacts in the G residues belonging to a short box, 5' CTTCC 3', positioned between -53 and -49 from the capsite. An additional factor, XrpFII, makes contacts with the sequence 5'GCCTGTTCGCC 3' located between -27 and -17 from the capsite. The deletion mutant still containing this sequence is poorly transcribed, but resumes activity when a short fragment containing the binding site for factor XrpFI is cloned in an upstream position.

Expression of ribosomal protein genes and regulation of ribosome biosynthesis in Xenopus development

Studies on ribosome biosynthesis in developing Xenopus oocytes and embryos, and after microinjection of cloned ribosomal-protein genes, have revealed that the synthesis of ribosomal proteins (r-proteins) is controlled by two types of regulation: (1) a post-transcriptional regulation, operated by feedback of the r-proteins themselves, controls processing and stability of r-protein transcripts and thus the amount of the corresponding mRNA present in the cell; and (2) a translational regulation controls the efficiency of utilization of r-protein mRNA (rp-mRNA) in response to the cellular needs for new ribosomes.

Isolation and nucleotide sequences of cDNAs for Xenopus laevis ribosomal protein S8: similarities in the 5' and 3' untranslated regions of mRNAs for various r-proteins

Recombinant clones specific for ribosomal protein (r-protein) S8 have been isolated from a Xenopus laevis cDNA bank. Sequence analysis shows that they are of two types, derived from two different gene copies originating from gene duplication. The two cDNAs differ in several silent sites and code for the same S8 protein whose complete amino acid sequence has been derived. Sequence comparison of S8 mRNAs with those for other X. laevis r-proteins, has revealed interesting similarities in the 5' and 3' untranslated regions. These could be involved in r-protein synthesis regulation which we have previously shown to occur mainly at post-transcriptional and translational levels.

Translational inactivation of ribosomal protein mRNAs during Xenopus oocyte maturation

Ribosomal protein synthesis ceases upon maturation of Xenopus oocytes. We find that this cessation results from the dissociation of ribosomal protein mRNAs from polysomes and is accompanied by the deadenylation of these transcripts. A synthetic mRNA encoding ribosomal protein L1, microinjected into stage VI oocytes, is deadenylated and released from polysomes upon maturation. Our results indicate that sequences located within 387 bp of the 3' terminus of L1 mRNA direct both the deadenylation and polysomal release of this ribosomal protein mRNA. The proper translational regulation of an exogenous ribosomal protein mRNA in microinjected oocytes provides a basis for determining the sequence specificity for the differential utilization of maternal mRNAs during oocyte maturation.

The primary structure of rat ribosomal protein L18

The amino acid sequence of rat ribosomal protein L18 was deduced from the sequence of nucleotides in a recombinant cDNA and confirmed from the amino-terminal amino acid sequence of the protein. Ribosomal protein L18 contains 187 amino acids (the amino-terminal methionine is removed after translation of the mRNA) and has a molecular weight of 21,530. Hybridization of the cDNA to digests of nuclear DNA suggests that there are 10-14 copies of the L18 gene. Rat ribosomal protein L18 is homologous to Xenopus laevis L14; the extent of the identity of the amino acid sequences is 87% and for the nucleotides in the coding region of the DNA it is 76%.

Nucleotide sequence and characterization of the transcript of a Dictyostelium ribosomal protein gene

Dictyostelium ribosomal protein mRNAs are subject to developmental regulation of both their translation and their stability. In order to consider whether such post-transcriptional regulation can be attributed to structural features of the mRNAs, we have cloned and sequenced a 1.9 kb EcoRI genomic DNA fragment which contains the gene for the Dictyostelium ribosomal protein 1024 (rp1024). The rp1024 gene contains a single intron of 350 bp which begins just after the fourth codon of protein coding sequence. Transcription begins 11 to 28 bp upstream from the initiator ATG in a pyrimidine rich region which is preceded by an oligo(dT)10 stretch, but which lacks a TATA box in the expected position. Processing of the 3' end occurs at either of two sites, resulting in two types of transcript which are present in equimolar amounts in both vegetatively growing and developing cells. Therefore, their relative abundance shows no correlation with the changes in translatability and stability of r-protein mRNAs which occur during development. A comparison of the sequence of the 5'-untranslated region of rp1024 mRNA to those of other Dictyostelium mRNAs shows that it differs significantly, primarily in its relatively high G+C content.

Rat ribosomal protein L35a multigene family: molecular structure and characterization of three L35a-related pseudogenes

The rat ribosomal protein L35a gene comprises a multigene family which contains 15-20 members as shown by the Southern blot analysis using L35a cDNA as a probe. We isolated 15 independent clones which contained distinct genes from a rat genomic library. Analysis of the restriction sites showed that all of them lacked the intervening sequences. Thermal stability of the hybrid molecules between these genes and the cDNA indicated that the similarity of the genes to the cDNA sequence varied. The nucleotide sequences of three genes gRL35a-A, gRL35a-B and gRL35a-G were determined. They shared some characteristics; namely: they lacked the intervening sequences, they contained (A)-rich tracts, and they were flanked by direct repeats. Two genes, gRL35a-A and gRL35a-B, contained a sequence completely identical to that of the cDNA. The nucleotide sequence of the 5' flanking region of gRL35a-B showed a significant homology with that of the same region of mouse ribosomal protein L32-related unmutated processed genes. Although this region of gRL35a-B contained the sequences homologous to the TATA box and the CCAAT box, gRL35a-B was not transcribed in an in vitro assay system. Thus, the L35a gene family comprises mostly processed pseudogenes. Further, Southern blot analysis in various animals indicated that the multigene construction of this ribosomal protein gene was a feature of mammalian genes. The origin and the evolutionary aspect of processed pseudogenes are discussed.