Transcriptional analysis and mutation of a dnaA-like gene in Synechocystis sp. strain PCC 6803

Transcription of the dnaA gene of the cyanobacterium Synechocystis sp. strain PCC 6803 is light dependent and yields a monocistronic mRNA, as determined by Northern analysis. Surprisingly, mutants with inactivated dnaA were viable. In batch cultures under standard conditions, the mutants grew like the wild type and did not show an aberrant phenotype. We conclude that, unlike the situation in other bacteria, dnaA of Synechocystis sp. cannot have an essential function, such as initiation of DNA replication.