THE DCR GENE FAMILY OF DESULFOVIBRIO - IMPLICATIONS FROM THE SEQUENCEOF DCRH AND PHYLOGENETIC COMPARISON WITH OTHER MCP GENES

Desulfovibrio vulgaris Hildenborough contains a family of genes for me thyl-accepting chemotaxis proteins (MCPs). Here we report the complete sequence of the gene for Desulfovibrio chemoreceptor H (dcrH). The de duced amino acid sequence of DcrH protein, which has an enlarged N-ter minal, ligand binding domain, indicates a structure similar to that of other MCPs. Comparison of the sequences for DcrA, determined earlier, and DcrH indicated that similarity is essentially limited to the C-te rminal excitation region. The dcr gene family differs, in this respect , from mcp gene families in other eubacteria (e.g. Escherichia coli an d Bacillus subtilis), where MCPs share significant homology throughout their C-terminal signal transduction domains. This may point to an an cient evolutionary origin of the dcr gene family, which is widely dist ributed throughout the genus Desulfovibrio. The evolutionary origin of mcp genes was traced by comparing nucleotide sequences for the excita tion region that is common to all MCPs. Phylogenetic analysis of seque nces for thirty mcp genes from nine eubacterial and one archaebacteria l species suggested that multiplication of mcp genes has occurred at l east twice since the eubacteria diverged from the archaebacteria.