The genes for yeast ribosomal proteins S24 and L46 are adjacent and divergently transcribed

Unlike most yeast ribosomal protein genes studied so far the genes coding for S24 and L46 are adjacent on the genome. Sequence analysis showed that the two genes are transcribed divergently, their initiation codons being 630 bp apart. Taking the respective ATG translation start sites as reference points, the 5'- end of L46 mRNA was mapped at position -26, while the S24 mRNA showed two major 5'-ends mapping at positions -13 and -16 respectively. Unlike most other yeast ribosomal protein genes, the gene for S24 does not contain an intron. Its coding region encompasses 390 nucleotides encoding a protein of 14762 D. The gene for L46 on the other hand is split by an intron of 386 nucleotides starting after its second codon. This gene encodes a small, very basic protein having a molecular weight of 6334 D. Yeast ribosomal proteins S24 and L46 show striking homologies with ribosomal proteins from other organisms. In particular, yeast L46 is clearly the evolutionary counterpart of rat liver L39. A search of the intergenic region for sequence elements previously identified as common to most yeast ribosomal protein genes, revealed the presence of a single conserved box (RPG-box) roughly equidistant from the transcription initiation sites of both genes. We suggest that this box acts as a regulatory signal in either orientation and thus influences the expression of both genes simultaneously.