THE SEQUENCES OF HEAT-SHOCK-PROTEIN-40 (DNAJ) HOMOLOGS PROVIDE EVIDENCE FOR A CLOSE EVOLUTIONARY RELATIONSHIP BETWEEN THE DEINOCOCCUS-THERMUS GROUP AND CYANOBACTERIA

The genes encoding for heat shock protein 40 (Hsp40 or DnaJ) homologs were cloned and sequenced from the archaebacterium Halobacterium cutir ubrum and the eubacterium Deinococcus proteolyticus to add to sequence s from the gene banks. These genes were identified downstream of the H sp70 (or DnaK) genes in genomic fragments spanning this region and, as in other prokaryotic species, Hsp70-Hsp40 genes are likely part of th e same operon. The Hsp40 homolog from D. proteolyticus was found to be lacking a central 204 base pair region present in H. cutirubrum that encodes for the four cysteine-rich domains of the repeat consensus seq uence CxxCxGxG (where x is any amino acid), present in most Hsp40 homo logs. The available sequences from various archaebacteria, eubacteria, and eukaryotes show that the same deletion is also present in the hom ologs from Thermus aquaticus and two cyanobacteria, but in no other sp ecies tested. This unique deletion and the clustering of homologs from the Deinococcus-Thermus group and cyanobacterial species in the Hsp40 phylogenetic trees suggest a close evolutionary relationship between these groups as was also shown recently for Hsp70 sequences (R.S. Gupt a et al., J Bacteriol 179:345-357, 1997). Sequence comparisons indicat e that the Hsp40 homologs are not as conserved as the Hsp70 sequences. Phylogenetic analysis provides no reliable information concerning evo lutionary relationship between prokaryotes and eukaryotes and their us efulness in this regard is limited. However, in phylogenetic trees bas ed on Hsp40 sequences, the two archaebacterial homologs showed a polyp hyletic branching within Grampositive bacteria, similar to that seen w ith Hsp70 sequences.