SEQUENCE OF THE CDNA AND GENE CODING FOR RIBOSOMAL-PROTEIN S1 OF XENOPUS-LAEVIS

The cloning and complete sequencing of one of the two gene copies codi ng for ribosomal protein (r-protein) S1 in Xenopus laevis and of the c orresponding cDNA are reported. The comparison of the sequence of this cDNA (S1b) with the other (S1a) previously reported, reveals that, wh ile the two DNA sequences have diverged somewhat, the amino-acid seque nces are mostly unchanged. The two gene copies are apparently expresse d at comparable levels, since the two corresponding mRNAs are similary represented in oocyte poly(A) RNA. The S1b gene has a total length of about 12 000 nt and is composed of seven exons and six introns. By pr imer extension, it has been determined that the transcription start po int is located in a pyrimidine-rich tract, as observed for all r-prote in genes of X. laevis and other vertebrates so far analyzed. A compute r analysis of the S1 sequence has shown the presence of a 150-nt seque nce repeated in introns 3, 5 and 6, which is homologous to the one rep orted in the first intron of mammalian r-protein S3 gene. Furthermore, a 130-nt sequence is tandemly repeated 2.5 times at each of the two s ites near the beginning and near the end of the first intron.