SAV, an archaebacterial gene with extensive homology to a family of highly conserved eukaryotic ATPases.

Nucleotide sequencing of a region of the hyperthermophilic archaebacterium Sulfolobus acidocaldarius allowed us to identify an open reading frame of 780 amino acids strikingly similar to a family of eukaryotic ATPases, involved in a variety of biological functions. Sequence analysis of the predicted polypeptide revealed 63 to 66% similarity with S. cerevisiae CDC 48p and its related genes in amphibians (p97ATPase) and mammals (Valosin Containing Protein, VCP), all possibly involved in the regulation of the cell cycle. The finding of an archaebacterial equivalent of these proteins with a high degree of similarity suggests that it represents the same gene in these various species. The new archaebacterial ORF, called SAV (S. acidocaldarius VCP-like) exhibited the usual signature of all members of the family, a highly conserved domain of about 200 amino acids, which is duplicated. Thus, apart from the VCP-like proteins, SAV also appeared similar, although less clearly, to other ATPases, members of the family, involved in vesicle-mediated transport (NSF, Sec18p), peroxysome assembly (PAS1p), and gene expression in yeast (SUG1p) and in human immunodeficiency virus (TBP-1). Finally, the discovery of the archaebacterial gene could enlighten not only the evolutionary relationships between the members of this complex ATPase family, but also the cellular function of these proteins, that is presently obscure.