EXPRESSION AND REGULATION OF A DNAA HOMOLOG ISOLATED FROM PSEUDOMONAS-PUTIDA

A gene homologous to the Escherichia coli dnaA gene was isolated from Pseudomonas putida and its transcription was investigated in E. coli as well as in P. putida. In both species the P. putida dnaA gene is transcribed from two promoters, one of which shows strong homology to promoters recognized by the sigma-54 factor found in both bacteria. In E. coli transcription of the P. putida dnaA gene can be repressed by overproduction of E. coli DnaA protein, presumably due to the presence of several DnaA-box-like sequences found in the promoter region. Likewise the P. putida DnaA protein is able to regulate expression of the E. coli dnaA gene but we failed to demonstrate autoregulation of the P. putida dnaA gene. A point mutation was introduced into the P. putida dnaA gene, equivalent to the ATP binding site mutation present in E. coli dnaA5 and dnaA46 mutants, and this alteration abolished the ability of the protein to repress the expression of the E. coli dnaA gene. These results indicate that DnaA proteins from other species than E. coli have maintained the ability to recognize the DnaA box sequence and that the conservation between the DnaA proteins reflects functionally similar domains.