Ribosomal protein L7a is encoded by a gene (Surf-3) within the tightly clustered mouse surfeit locus

Surf4, cargo trafficking, lipid metabolism, and therapeutic implications

Surfeit 4 is a polytopic transmembrane protein that primarily resides in the endoplasmic reticulum (ER) membrane. It is ubiquitously expressed and functions as a cargo receptor, mediating cargo transport from the ER to the Golgi apparatus via the canonical coat protein complex II (COPII)-coated vesicles or specific vesicles. It also participates in ER-Golgi protein trafficking through a tubular network. Meanwhile, it facilitates retrograde transportation of cargos from the Golgi apparatus to the ER through COPI-coated vesicles. Surf4 can selectively mediate export of diverse cargos, such as PCSK9 very low-density lipoprotein (VLDL), progranulin, α1-antitrypsin, STING, proinsulin, and erythropoietin. It has been implicated in facilitating VLDL secretion, promoting cell proliferation and migration, and increasing replication of positive-strand RNA viruses. Therefore, Surf4 plays a crucial role in various physiological and pathophysiological processes and emerges as a promising therapeutic target. However, the molecular mechanisms by which Surf4 selectively sorts diverse cargos for ER-Golgi protein trafficking remain elusive. Here, we summarize the most recent advances in Surf4, focusing on its role in lipid metabolism.

Preservation of ranking order in the expression of human Housekeeping genes

Housekeeping (HK) genes fulfill the basic needs for a cell to survive and function properly. Their ubiquitous expression, originally thought to be constant, can vary from tissue to tissue, but this variation remains largely uncharacterized and it could not be explained by previously identified properties of HK genes such as short gene length and high GC content. By analyzing microarray expression data for human genes, we uncovered a previously unnoted characteristic of HK gene expression, namely that the ranking order of their expression levels tends to be preserved from one tissue to another. Further analysis by tensor product decomposition and pathway stratification identified three main factors of the observed ranking preservation, namely that, compared to those of non-HK (NHK) genes, the expression levels of HK genes show a greater degree of dispersion (less overlap), stableness (a smaller variation in expression between tissues), and correlation of expression. Our results shed light on regulatory mechanisms of HK gene expression that are probably different for different HK genes or pathways, but are consistent and coordinated in different tissues.

The human homologue of the mouse Surf5 gene encodes multiple alternatively spliced transcripts

Hu-Surf5 is included within the Surfeit locus, a cluster of six genes originally identified in mouse. In the present study, we have cloned and characterized the Hu-Surf5 gene and its mRNA multiple transcripts. Comparison of the most abundant cDNA and genomic sequence shows that the Hu-Surf5 is spread over a region of approximately 7.5 kb and consists of five exons separated by four introns. The nucleotide sequence of the genomic region flanking the 3'-end of the Hu-Surf5 gene revealed the presence of a processed pseudogene of human ribosomal protein L21 followed by Hu-Surf6 gene. Only 110 bp separate the transcription start site of Hu-Surf5 and Hu-Surf3/L7a gene and the transcription direction is divergent. Earlier studies defined the 110 bp region essential for promoter activity of Hu-Surf3/L7a. Here, we show that this region stimulates transcription with a slightly different efficiency in both directions. The bidirectional promoter lacks an identifiable TATA box and is characterized by a CpG island that extends through the first exon into the first intron of both genes. These features are characteristic of housekeeping genes and are consistent with the wide tissue distribution observed for Hu-Surf5 expression. Hu-Surf5 encodes three different transcripts, Surf-5a, Surf-5b, and Surf-5c, which result from alternative splicing. Two protein products, SURF-5A and SURF-5B have been characterized. Production of chimaeras between the full-length SURF-5A or SURF-5B and the green fluorescent protein (GFP) allowed to localize both proteins in the cytoplasm.

Isolation and genomic analysis of the human surf-6 gene: a member of the Surfeit locus

The human Surfeit locus contains at least six tightly clustered genes (Surf-1 to Surf-6) of which five (Surf-1 to Surf-5) have been characterised and found not to share any sequence homology. The organisation and juxtaposition of the Surfeit genes are conserved between human and mouse. The Surf-6 gene that encodes a novel nucleolar-matrix protein with nucleic-acid binding properties has been characterised in mouse. In this work, we have isolated and analysed the human Surf-6 homologue and determined its genomic organisation in the Surfeit locus. The human Surf-6 gene has five exons spread over a distance of 4.3kb and has features of a housekeeping gene being ubiquitously expressed, having its 5' end located within a CpG rich island and lacking a canonical TATA box. The intragenic region between the 3' end of the Surf-5 gene and the 5' end of the Surf-6 gene is 3.2kb and contains a pseudogene of the ribosomal protein gene rpL21. The putative human Surf-6 protein is 361 amino acids long and includes motifs found in both the mouse and fish Surf-6 homologues, which may underlie the functions of Surf-6. Three amino acid polymorphisms have been detected at codons 163, 175 and 311 by SSCP analysis.

SURFEIT-1 gene analysis and two-dimensional blue native gel electrophoresis in cytochrome c oxidase deficiency

Leigh syndrome, a progressive, often fatal, neurodegenerative disorder, is frequently associated with a deficiency in the activity of cytochrome c oxidase (COX), the last enzyme of the mitochondrial respiratory chain. In contrast to NADH:ubiquinone oxidoreductase and succinate dehydrogenase deficiencies, no mutations in nuclear genes encoding COX subunits have been identified thus far. Very recently, however, a Leigh syndrome complementation group has been identified which showed mutations in the SURFEIT-1 (SURF-1) gene. The results of a mutational detection study in 16 new randomly selected COX-deficient patients revealed a new mutation (C688T) in 2 patients and the earlier reported 845delCT mutation in 2 additional patients. In addition, we evaluated the diagnostic value of two-dimensional blue native gel electrophoresis. We show that this technique reveals distinct patterns of both fully and partially assembled COX complexes and is thereby capable of discrimination between COX-deficient SURF-1 and non-SURF-1-mutated patients.

SURF1, encoding a factor involved in the biogenesis of cytochrome c oxidase, is mutated in Leigh syndrome

Leigh Syndrome (LS) is a severe neurological disorder characterized by bilaterally symmetrical necrotic lesions in subcortical brain regions that is commonly associated with systemic cytochrome c oxidase (COX) deficiency. COX deficiency is an autosomal recessive trait and most patients belong to a single genetic complementation group. DNA sequence analysis of the genes encoding the structural subunits of the COX complex has failed to identify a pathogenic mutation. Using microcell-mediated chromosome transfer, we mapped the gene defect in this disorder to chromosome 9q34 by complementation of the respiratory chain deficiency in patient fibroblasts. Analysis of a candidate gene (SURF1) of unknown function revealed several mutations, all of which predict a truncated protein. These data suggest a role for SURF1 in the biogenesis of the COX complex and define a new class of gene defects causing human neurodegenerative disease.

The human Surfeit locus

The organization of the human Surfeit locus containing the six sequence-unrelated housekeeping genes Surf-1 to Surf-6 (HGMW-approved symbols SURF1-SURF6) has been determined. The human surfeit locus occupies about 60 kb of DNA, and the tightly clustered gene organization and the juxtaposition of the human genes are similar to the mouse and chicken surfeit loci with the 5' end of each gene associated with a CpG-rich island. Whereas in the mouse the Surf-2 and Surf-4 genes overlap at their 3' ends, the human Surf-2 and Surf-4 genes have been found to be separated by 302 bp due to a much shorter 3' untranslated region in the human Surf-2 gene. The distance between the 3' ends of the human Surf-1 and Surf-3 genes is 374 bp, and the distance between the 5' ends of the human Surf-3 and Surf-5 genes is only 112 bp. Unusually the human Surf-5 gene contains an intron in its 5' untranslated region not found in the mouse or rat Surf-5 genes. This additional intron is also found in the Surf-5 gene of both Old and New World monkeys, being generated before the divergence of human and prosimians but after the divergence of primates and rodents. A contig of 200 kb containing the human Surfeit locus has been constructed from overlapping cosmid, P1, and PAC clones. Approximately 40 kb proximal to the 3' end of the Surf-6 gene, the 5' region of the ABO glycosyltransferase gene has been detected. This allows us to determine the orientation of the Surfeit and ABO loci with respect to each other and to the telomere and centromere of human chromosome 9.

The gene for ribosomal protein L7a-1 in Schizosaccharomyces pombe contains an intron after the initiation codon

The gene encoding ribosomal protein L7a-1 in the fission yeast Schizosaccharomyces pombe is identified by the similarity of its open reading frame to the respective gene in Saccharomyces cerevisiae. The L7a gene is encoded in two different genomic environments as frequently found for ribosomal protein genes in this organism. One of these genes, L75a-1, is located on chromosome 2. The two consensus promoter elements homol D and homol E are both identified upstream of the start codon of this gene. The ATG start codon is separated from the main reading frame by an intron of 66 nucleotides.

The comparative genomic structure and sequence of the surfeit gene homologs in the puffer fish Fugu rubripes and their association with CpG-rich islands

The puffer fish Fugu rubripes (Fugu) has a compact genome approximately one-seventh the size of man, mainly owing to small intron size and the presence of few dispersed repetitive DNA elements, which greatly facilitates the study of its genes at the genomic level. It has been shown previously that, whereas the Surfeit genes are tightly clustered at a single locus in mammals and birds, the genes are found at three separate loci in the Fugu genome. Here, Fugu gene homologs of all six Surfeit genes (Surf-1 to Surf-6) have been cloned and sequenced, and their gene structure has been compared with that of their mammalian and avian homologs. The predicted protein products of each gene are well conserved between vertebrate species, and in most cases their gene structures are identical to their mammalian and avian homologs except for the Fugu Surf-6 gene, which was found to lack an intron present in the mouse gene. In addition, we have identified conserved regulatory elements at the 5' and 3' ends of the Surf-3/rpL7a gene by comparison with the mammalian and chicken Surf-3/rpL7a gene homologs, including the presence of a polypyrimidine tract at the extreme 5' end of this ribosomal protein gene. The Fugu Surfeit gene homologs appear to be associated with CpG-rich islands, like the Surfeit genes in higher vertebrates, but these Fugu CpG islands are similar to the nonclassical islands characteristic of other fish species. Our observations support the use of the Fugu genome to study vertebrate gene structure, to predict the structure of mammalian genes, and to identify vertebrate regulatory elements. [The sequence data described in this paper have been submitted to the data library under accession nos. Y15170 (Surf-2, Surf-4), Y15171 (Surf-3, Surf-1, Surf-6), and Y15172 (Surf-5.)]

Structure and expression of two highly related genes encoding SCM-1/human lymphotactin

SCM-1/lymphotactin is a chemokine-like molecule produced selectively, if not exclusively, by activated CD8+ T cells. Here we report that there are two highly homologous SCM-1 genes, which we designate as SCM-1alpha and SCM-1beta. Both genes have three exons and two introns. The 1st intron of SCM-1alpha contains a pseudogene of the ribosomal large subunit L7a. In SCM-1beta, a 1.5-kb region including about a quarter of the L7a pseudogene is deleted from the 1st intron. Otherwise, the two genes are highly homologous including the 5' and 3' flanking regions. Both genes were mapped to human chromosome 1q23. The two genes were similarly induced in peripheral blood mononuclear cells by mitogenic stimulation. Primer extension and RNase protection revealed several transcription initiation sites. The biological activities of SCM-1alpha and SCM-1beta, which have two amino acid differences at positions 7 and 8 in the mature proteins, remain to be compared.

The Surf-6 gene of the mouse surfeit locus encodes a novel nucleolar protein

The Surfeit locus contains the tightest cluster of mammalian genes so far described. The five Surfeit genes (Surf-1 to -5) that have been previously isolated and characterized do not share any DNA or amino acid sequence homology. These Surfeit genes appear to be housekeeping genes, with the Surf-3 gene encoding the 1.7a ribosomal protein and the Surf-4 gene encoding an integral membrane protein most likely associated with the endoplasmic reticulum. In this work, we have isolated the Surf-6 gene, a sixth member of the Surfeit locus. The Surf-6 gene contains four exons spanning a genomic region of 14 kb and specifies a mRNA of 2,571 bases. Surf-6 has features common to housekeeping genes because its transcript is present in every tissue tested, its 5' end is associated with a CpG-rich island, and its promoter does not contain a canonical TATA box. The Surf-6 long open reading frame encodes a novel highly basic polypeptide of 355 amino acids (28% Arg and Lys). By immunofluorescence and immunoblot analyses, the Surf-6 protein has been found to be located in the nucleolus and by immunocytochemical microscopy to be localized predominantly in the nucleolar granular component, a structure that is involved in ribosome maturation. These results indicate that the novel Surf-6 gene is involved in a nucleolar function.

The surf-4 gene encodes a novel 30 kDa integral membrane protein

The mouse surfeit locus is a tight cluster of at least six genes (surf-1 to -6), unrelated by sequence homology, whose unique organization is conserved in vertebrates. We show that the surf-4 coding sequence is conserved between mouse and human. Primary sequence analysis predicts that the mouse surf-4 protein contains seven transmembrane domains and a double lysine endoplasmic reticulum (ER) retrieval motif on the carboxyl terminus. Translation of the mouse surf-4 cDNA in vitro resulted in the production of a 30 kDa membrane protein. Salt and detergent extraction procedures showed that the surf-4 protein associated tightly with the microsomal membranes. Proteolysis protection of 14 and 3 kDa fragments indicates that the surf-4 protein contains at least two membrane spanning domains: this is consistent with the proposed topology. Addition of the c-Myc epitope into three different regions of the surf-4 protein resulted in transfectants that expressed a myc-tagged protein. Immunofluorescence analysis of the three surf-4 myc chimeras yielded a cytoplasmic staining pattern. Consistent with the presence of the ER retrieval motif, the surf-4 myc protein was not detected at the plasma membrane. A model for the proposed structure of the surf-4 protein is presented.

Identification and genetic mapping of 151 dispersed members of 16 ribosomal protein multigene families in the mouse

More than 150 individual members of 16 ribosomal protein multigene families were identified as DNA restriction fragments and genetically mapped. The ribosomal protein gene-related sequences are widely dispersed throughout the mouse genome. Map positions were determined by analysis of 144 progeny mice from both an interspecific (C57BL/6J x SPRET/Ei)F1 x SPRET/Ei and an intersubspecific (C57BL/6J x CAST/Ei)F1 x C57BL/6J backcross. In addition, 30 members of the multigene families encoding PGK1 ODC, and TPI, including five new loci for ODC and one new locus for TPI, were characterized and mapped. Interspecific backcross linkage data for 29 nonecotropic murine leukemia retroviruses endogenous to C57BL/6J mice are also reported. Transmission ratio distortions and recombination frequencies are compared between the two backcrosses.

The primary structure of two proteins from the large ribosomal subunit of rice

We isolated two rice cDNAs which encode an open reading frame of 389 amino acids. Their deduced amino acid sequence corresponded to the ribosomal protein (r-protein). A comparison of amino acid sequence shows that the deduced amino acid sequence of one cDNA is homologous to Arabidopsis, yeast and the rat r-protein L3. Another encoded products with a high degree of homology to the rat r-protein L7A and yeast r-protein L4.

Human L7a ribosomal protein: sequence, structural organization, and expression of a functional gene

A cDNA coding for the human L7a ribosomal protein (r-protein) was used to isolate the corresponding gene by screening two human genomic libraries constructed in bacteriophage lambda and in a cosmid vector. One of the cosmid clones isolated, cos1.1, contains the whole L7 alpha gene, composed of eight exons and seven introns spanning 3226 bp. As in other mammalian housekeeping genes, the promoter and the first exon of the L7 alpha reside within a CpG-rich island. Furthermore, similar to the other higher eukaryote r-protein-encoding genes characterized so far, the human L7 alpha gene has a C as the major transcriptional start point localized in a pyrimidine-rich region and lacks a canonical TATA sequence. We show that 130 bp of the human L7 alpha gene 5'-flanking region represent the minimal element required to promote its transcription. This element is strikingly conserved between the mouse and human L7 alpha genes. Finally, a comparison of the human L7 alpha gene coding sequence and the predicted amino acid (aa) sequence with the sequences of mouse L7a, rat L7a, and the homologous yeast L4 shows that the aa sequence has been highly conserved during evolution.

The complete nucleotide sequence of chicken ribosomal protein L7a gene and the multiple factor binding sites in its 5'-flanking region

The nucleotide sequence of the gene encoding chicken ribosomal protein L7a was determined. The gene contains eight exons and seven introns, which spread over 3613 nucleotides. The transcription initiation sites were located on four consecutive nucleotides GCCC, which are at the 5' terminus of a short polypyrimidine tract of eight base-pairs flanked by G + C-rich regions. Neither a canonical TATA nor a CAAT box was found in the 5'-flanking region. Instead, a short A + T-rich stretch was found at the position where the TATA box is expected to be. There is an intensive nuclear protein binding motif repeated four times in the region -134 to -50. This motif is common to many ribosomal protein genes and may play an important role in the control of ribosomal protein gene expression.

The mapping of seven intron-containing ribosomal protein genes shows they are unlinked in the human genome

Mammalian ribosomal protein (rp) genes are members of multigene families which are composed predominantly of multiple processed pseudogenes and one functional intron-containing gene. The presence of multiple pseudogenes has hampered the isolation and study of the functional rp genes. We have recently developed a polymerase chain reaction (PCR)-based strategy for the detection of intron-containing genes in the presence of multiple pseudogenes (B. Davies, S. Feo, E. Heard, and M. Fried, 1989, Proc. Natl. Acad. Sci. USA 86: 6691-6695). We have used this technique to identify the intron-containing PCR products of seven human rp genes (rpL19, rpL30, rpL35a, rpL36a, rpS6, rpS11, rpS17) and to map their chromosomal locations. No linkage was found between any of these seven rp genes nor was linkage found to the three other rp genes previously mapped. The wide distribution of the rp genes throughout the human genome strongly suggests that the coordinate regulation of the expression of mammalian ribosomal proteins in response to the cell's varying requirements for protein synthesis is not a result of cis activation of chromosomal regions but is mediated by trans-acting factors.

Expression of ribosomal protein genes in mouse oocytes and early embryos

The quantitative changes in the mRNAs for ribosomal proteins L7a, L18a, and S15 were assayed in slot hybridization experiments using labeled cRNA probes with total RNA from late growth-phase oocytes, ovulated eggs, and early embryos through the blastocyst stage. All three mRNAs showed a similar developmental pattern of prevalence, but their copy numbers per oocyte or embryo fluctuated according to developmental stage. There are on an average about 17,000 copies of each mRNA in the late growth-phase oocyte; this number drops to one-fifth to one-tenth in the ovulated egg and two-cell embryo but increases rapidly during cleavage to bout 25,000 in the eight-cell embryo and about 42,000 in the blastocyst. A comparison of the levels of these mRNAs with the reported rates of ribosomal protein synthesis (LaMarca and Wassarman, 1979) suggests that, in late growth-phase oocytes, ribosomal protein synthesis is regulated primarily at the translational level and is kept low by some factor limiting mRNA utilization. On the other hand, the high rate of ribosome biosynthesis during early embryogenesis from the two-cell stage onward appears to involve the coordinate activation and transcription of ribosomal RNA and ribosomal protein genes coupled with the immediate translational utilization of ribosomal protein mRNAs.

The organization and expression of the human L7a ribosomal protein gene

The genomic structure and sequence of the human ribosomal protein L7a (rpL7a) and its transcriptional start sites have been determined. The gene contains eight exons and seven introns spread over 3179 bp. The human rpL7a gene is similar to other mammalian ribosomal protein genes in containing a short first exon, a short 5' untranslated leader and its transcriptional start sites at C residues embedded in a polypyrimidine tract. The 25 bp polypyrimidine tract containing the two human rpL7a start sites is the longest polypyrimide tract so far observed for a mammalian ribosomal protein gene.

The organization and expression of the Saccharomyces cerevisiae L4 ribosomal protein genes and their identification as the homologues of the mammalian ribosomal protein gene L7a

A cDNA for the mouse ribosomal protein (rp) L7a, formerly called Surf-3, was used as a probe to isolate two homologous genes from Saccharomyces cerevisiae. The two yeast genes (L4-1 and L4-2) were identified as encoding S. cerevisiae L4 by 2D gel analysis of the product of the in vitro translation of hybrid-selected mRNA and additionally by direct amino acid sequencing. The DNA sequences of the two yeast genes were highly homologous (95%) over the 771 bp that encode the 256 amino acids of the coding regions but showed little homology outside the coding region. L4-1 differed from L4-2 by 7 out of the 256 amino acids in the coding region, which is the greatest divergence between the products of any two duplicated yeast ribosomal protein genes so far reported. There is strong homology between the mouse rpL7a/Surf-3 and the yeast L4 genes -57% at the nucleic acid level and also 57% at the amino acid level (though some regions reach as much as 80-90% homology). While most yeast ribosomal protein genes contain an intron in their 5' region both L4-1 and L4-2 are intronless. The mRNAs derived from each yeast gene contained heterogenous 5' and 3' ends but in each case the untranslated leaders were short. The L4-1 mRNA was found to be much more abundant than the L4-2 mRNA as assessed by cDNA and transcription analyses. Yeast cells containing a disruption of the L4-1 gene formed much smaller colonies than either wild-type or disrupted L4-2 strains. Disruption of both L4 genes is a lethal event, probably due to an inability to produce functional ribosomes.

Developmental changes of neuron-specific enolase mRNA in primary cultures of rat neurons

1. The level of mRNAs for neuron-specific enolase (NSE) and nonneuronal enolase (NNE) was studied in developing rat brain and in pure neuronal cultures of corresponding ages treated or not treated with triiodothyronine (T3). 2. In brain cortices both messages are already detectable at the earliest age (embryonal day 16; E16). During development the mRNA for NNE remains at a steady level, with a transient decline at postnatal day 5 (P5). 3. On the other hand, NSE mRNA follows a biphasic curve: the signal increases threefold from E-16 to P0 and threefold from P5 to P18, with a plateau between P0 and P5. 4. In neuronal cultures the NNE message is present at a constant level until day 10 and declines sharply thereafter, while in T3-treated cultures it reaches a minimum beforehand. 5. The NSE mRNA, on the other hand, increases continuously throughout the whole culture life span, and a slightly higher level is observed in T3-treated cells during the first ten days.

The HOX-5 and surfeit gene clusters are linked in the proximal portion of mouse chromosome 2

Using an interspecies backcross, we have mapped the HOX-5 and surfeit (surf) gene clusters within the proximal portion of mouse chromosome 2. While the HOX-5 cluster of homeobox-containing genes has been localized to chromosome 2, bands C3-E1, by in situ hybridization, its more precise position relative to the genes and cloned markers of chromosome 2 was not known. Surfeit, a tight cluster of at least six highly conserved "housekeeping" genes, has not been previously mapped in mouse, but has been localized to human chromosome 9q, a region of the human genome with strong homology to proximal mouse chromosome 2. The data presented here place HOX-5 in the vicinity of the closely linked set of developmental mutations rachiterata, lethargic, and fidget and place surf close to the proto-oncogene Abl, near the centromere of chromosome 2.

Thyrotropin-induced expression of a gene for a ribosomal protein related to the trk oncogene

By differential screening of an FRTL5 rat thyroid cell cDNA library, we isolated a clone (G7) corresponding to an mRNA transcript whose steady-state level is increased by thyrotropin (TSH) stimulation by a non-transcriptional mechanism. The nucleotide sequence of the G7 cDNA (0.85 kb) revealed homology with two other genes. First, there was 89% homology with the cDNA for a protein whose amino-terminal end forms the amino terminus of the chimeric tyrosine kinase human oncogene, trk-2h. Second, TSH-responsive G7 is 95% homologous with the 'surf-3' gene within the mouse surfeit locus which codes for the mouse L7a ribosomal protein. These findings are of interest in view of the frequent occurrence in thyroid cancers of an oncogene (PTC) that consists of an unidentified amino terminus linked to a downstream tyrosine kinase moiety.

Oncogenic activation of the human trk proto-oncogene by recombination with the ribosomal large subunit protein L7a

The trk-2h oncogene, isolated from the human breast carcinoma cell line MDA-MB 231 by genomic DNA-transfection into NIH3T3 cells, consists of the trk proto-oncogene receptor kinase domain fused to a N-terminal 41 amino acid activating sequence (Kozma, S.C., Redmond, S.M.S., Xiao-Chang, F., Saurer, S.M., Groner, B. and Hynes, N.E. (1988) EMBO J., 7, 147-154). Antibodies raised against a bacterially produced beta gal-trk receptor kinase fusion protein recognized a 44 kd phosphoprotein phosphorylated on serine, threonine and tyrosine in extracts of trk-2h transformed NIH3T3 cells. In vitro, in the presence of Mn2+/gamma ATP, this protein became phosphorylated extensively on tyrosine. Cells transformed by trk-2h did not, however, show an elevation in total phosphotyrosine. We have cloned and sequenced the cDNA encoding the amino terminal activating sequences of trk-2h (Kozma et al., 1988). The encoded protein has a high basic amino acid content and the gene is expressed as an abundant 1.2 kb mRNA in human, rat and mouse cells. Antipeptide antibodies raised against a C-terminal peptide recognized specifically a 30 kd protein on Western blots of human, rat and mouse cell extracts. Immunofluorescence revealed, in addition to granular cytoplasmic fluorescence, intense nucleolar staining. The high basic amino acid content and nucleolar staining prompted us to investigate whether the 30 kd protein could be a ribosomal protein. Western immunoblotting analysis of 2D-electrophoretically resolved ribosomal proteins indicated that the 30 kd protein is the ribosomal large subunit protein L7a.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of the Surfeit gene cluster containing the ribosomal protein gene L7a to chromosome bands 9q33-34

The Surfeit gene cluster which contains at least four very tightly spaced unrelated genes, one of which encodes the ribosomal protein L7a, has been localized by an analysis of somatic cell hybrids to the long arm of chromosome 9. By the use of in situ hybridization the Surfeit locus has been further mapped to 9q33-34.