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 coding for ribosomal protein (r-protein) S1 in Xenopus laevis and of the corresponding cDNA are reported. The comparison of the sequence of this cDNA (S1b) with the other (S1a) previously reported, reveals that, while the two DNA sequences have diverged somewhat, the amino-acid sequences are mostly unchanged. The two gene copies are apparently expressed 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 12000 nt and is composed of seven exons and six introns. By primer extension, it has been determined that the transcription start point is located in a pyrimidine-rich tract, as observed for all r-protein genes of X. laevis and other vertebrates so far analyzed. A computer analysis of the S1 sequence has shown the presence of a 150-nt sequence repeated in introns 3, 5 and 6, which is homologous to the one reported 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 sites near the beginning and near the end of the first intron.