The evolutionary relationships between homologs of ribosomal YL8 protein and YL8-like proteins.

We previously reported the sequence of YL8A, one of the two genes encoding yeast ribosomal protein YL8. With the aim of conducting an evolutionary study we have cloned and sequenced a second gene, YL8B. The disruption of both genes is lethal. Unlike other duplicated ribosomal protein genes, each open reading frame is interrupted by two introns containing long conserved sequences. A comparison of nucleotide and amino-acid sequences reveals that the duplication of the YL8 gene must have occurred very recently. Alignment and phylogenetic analysis of the amino-acid sequences of YL8-related proteins from various species show the existence not only of YL8 ribosomal proteins but also of a family of YL8-like proteins. These are present in at least three species of yeast and seem to be functionally distinct from ribosomal proteins.