A gene has been cloned from the archaebacterium, Thermoplasma acidophilum, which, on the basis of the deduced amino acid sequence, encodes a homologue of the eukaryotic large subunit ribosomal proteins, L15/YL10. This gene, rpl15, was identified as an open reading frame (ORF) located 2.3 kb upstream of the gene encoding the alpha-subunit of the T. acidophilum proteasome. The putative translation product of rpl15 (RPL15) contains 197 amino acid residues, with a M(r) of 22,928 and a basic pI of 11.59. The RPL15 amino acid sequence shows significant similarity (> 35% identity) to the L15/YL10 proteins of various eukaryotes.