On the origin of Ser/Thr kinases in a prokaryote

The family of Ser/Thr and/or Tyr kinases and that of His kinases play essen tial roles in signal transduction. For a long time, the former has been fou nd in eukaryotes, the latter in prokaryotes. Studies in the last decade hav e shown, however, that most bacteria possess from one to more than 10 genes encoding Ser/Thr kinases. This observation raises an important question co ncerning the evolutionary origin of Ser/Thr kinases found in bacteria. To a nswer this question, we have analyzed a family of 11 genes encoding Ser/Thr kinases in the cyanobacterium Synechocystis sp. PCC 6803. This bacterium c ontains the largest number of Ser/Thr kinases among all bacteria whose geno mic sequences have been released so far. In this study, we have developed a user-friendly computer program for statistical analysis of codon usages an d GC content. The results demonstrate that Ser/Thr kinases have similar cod on usages and GC contents as the average of all possible open reading frame s (ORFs) deduced from the genome. In contrast, ORFs encoding transposases, as a control in our analysis, display a disparity in both codon usage and G C content, confirming their multiple origin and genetic promiscuity. In lig ht of our results, we propose that Ser/Thr kinases existed before the diver gence between prokaryotes and eukaryotes during evolution, or were laterall y transferred into prokaryotes at the early stages of bacterial evolution. If Ser/Thr kinases have persisted ever since in prokaryotes under evolution ary pressure, it is then expected that they play important, possibly even e ssential roles in regulating bacterial activities as do their counterparts in eukaryotes. (C) 2001 Federation of European Microbiological Societies. P ublished by Elsevier Science B.V. All rights reserved.