The structure and evolution of the ribosomal proteins encoded in the spc operon of the archaeon (Crenarchaeota) Sulfolobus acidocaldarius

The genes for nine ribosomal proteins, L24, L5, S14, S8, L6, L18, S5, L30, and L15, have been isolated and sequenced from the spe operon in the archae on (Crenarchaeota) Sulfolobus acidocaldarius, and the putative amino acid s equence of the proteins coded by these genes has been determined. In additi on, three other genes in the spc operon, coding for ribosomal proteins S4E, L32E, and L19E (equivalent to rat ribosomal proteins S4, L32, and L19), we re sequenced and the structure of the putative proteins was determined. The order of the ribosomal protein genes in the spc operon of the Crenarchaeot a kingdom of Archaea is identical to that present in the Euryarchaeota king dom of Archaea and also identical to that found in bacteria, except for the genes for r-proteins S4E, L32E, and L19E, which are absent in bacteria. Al though AUG is the initiation codon in most of the spc genes, GUG (val) and UUG (leu) are also used as initiation codons in S. acidocaldarius. Over 70% of the codons in the Sulfolobus ape operon have A or U in the third positi on, reflecting the low GC content of Sulfolobus DNA. Phylogenetic analysis indicated that the archaeal r-proteins are a sister group of their eucaryot ic counterparts but did not resolve the question of whether the Archaea is monophyletic, as suggested by the L6P, L15P, and L18P trees, or the questio n of whether the Crenarchaeota is separate from the Euryarchaeota and close r to the Eucarya, as suggested by the S8P, S5P, and L24P trees. In the case of the three Sulfolobus r-proteins that do not have a counterpart in the b acterial ribosome (S4E, L32E, and L19E), the archaeal r-proteins showed sub stantial identity to their eucaryotic equivalents, but in all cases the arc haeal proteins formed a separate group from the eucaryotic proteins. (C) 19 99 Academic Press.