Ribosomal protein S14 is encoded by a pair of highly conserved, adjacent genes on the X chromosome of Drosophila melanogaster.

Abstract

We describe a Drosophila DNA clone of tandemly duplicated genes encoding an amino acid sequence nearly identical to human ribosomal protein S14 and yeast rp59. Despite their remarkably similar exons, the locations and sizes of introns differ radically among the Drosophila, human, and yeast (Saccharomyces cerevisiae) ribosomal protein genes. Transcripts of both Drosophila RPS14 genes were detected in embryonic and adult tissues and are the same length as mammalian S14 message. Drosophila RPS14 was mapped to region 7C5-9 on the X chromosome. This interval also encodes a previously characterized Minute locus, M(1)7C.Although procaryotic and eucaryotic ribosomes display striking architectural differences (14-16), many ribosomal subunit components share substantial structural homology.Only recently has the extent of these relationships become apparent through comparison of analogous ribosomal protein genes from phylogenetically distant organisms. We have shown that two cloned human ribosomal protein genes, RPS14 and RPS17, detect significant nucleic acid homology among diverse genomic DNAs (6). Computer-aided analysis of nucleic acid and protein sequence data bases confirmed these homologies and further defined structural similarities shared by these two mammalian genes and their yeast (Saccharomyces cerevisiae) homologs. Mammalian S14 and yeast rp59 polypeptides are almost identical, as are mammalian S17 and yeast rpSl proteins (6). Homologies discerned among human and yeast ribosomal protein genes are restricted to coding sequences (exons) only, whereas the number, arrangement, and size of intervening sequences (introns) differ markedly.Previously we noted that Drosophila melanogaster DNA contains two PstI restriction fragments detectable with a human RPS14 cDNA probe (6). Because insects, yeasts, and mammals diverged early in the course of eucaryote evolution, and because D. melanogaster is amenable to detailed genetic and molecular analyses, we decided to characterize Drosophila RPS14. We anticipated that this information might provide significant clues into the evolutionary history of an important housekeeping gene family. In addition, we hoped to establish an experimental system suitable for detailed molecular and genetic analysis of ribosome biosynthesis in a higher eucaryote. Now we describe a Drosophila DNA clone which contains a tandemly duplicated pair of nearly identical RPS14 genes. Both S14 genes include a short intervening sequence at a position unrelated to the introns in yeast rp59 (32) and human RPS14 (28). Both Drosophila genes appear to be transcribed as monocistronic messages in adult tissues. The cloned DNA fragment has been mapped in situ to region 7C5-9 on the Drosophila X chromosome. In agreement with the notion that haplo-insufficient Minute mutations affect ribosomal protein genes in D. melanogaster (4,13,33) RNAs were isolated from Drosophila eggs and adults and from human (HeLa) cells by homogenization in guanidinium isothiocyanate and extraction with redistilled phenol and chloroform (7)...

A Drosophila ribosomal protein functions in mammalian cells.

“…2, lane Dros). S14 mRNA of the same size has been observed in embryonic insect tissues by using a variety of cloned DNA probes (4). Antisense insect RNA probe did not hybridize with Emr2-2 message (Fig.…”

“…Either the insect transcriptional promoter is not functional in CHO cells or DMGS14-1 does not include a complete promoter sequence. With respect to the latter possibility, it should be noted that DMGS14-1 includes both the RPS14A and the B genes as well as nearly 3 kbp of flanking chromosomal DNA sequence (4).…”

“…Nine of the differences involve radical amino acid replacements located almost exclusively (7 of 9) within the first 32 residues of the proteins. Complete protein-coding sequences of Chinese hamster, human, and Drosophila RPS14 can be found in GenBank under accession numbers M11241, M13934, and M21045, respectively.Nucleic acid and protein sequence similarities provide compelling evidence for stuctural homology among mammalian and Drosophila RPSJ4 loci (4,8). Because Chinese hamster RPSJ4 has been correlated with recessive emetine resistance mutations (EmtB) in somatic tissue culture cells (2,3,9,11,12,17,18,20,21), this locus offers a unique opportunity to examine conservation among eucaryotic rproteins and genes by using genetic as well as biochemical criteria.…”

“…We have isolated and sequenced transcriptionally active ribosomal protein (r-protein) S14 genes from Chinese hamster ovary (CHO) cells (16,20), human placenta (19,21), and Drosophila melanogaster (4). The human S14 gene (RPS14) maps to chromosome 5q23-33 (15,19), and the Chinese hamster gene maps to chromosome 2q (5,6).…”

“…Drosophila RPS14 is located on the X chromosome in region 7C5-9 (4). The gene consists of a tandemly duplicated pair of transcriptionally active genes (4), both of which encode exactly the same r-protein. Insect S14 protein differs from its mammalian homologs at 20 of 151 amino acid residues.…”