Autorepression of the dnaA Gene of Escherichia Coli

Abstract

The dnaA protein is essential for initiation of replication from the chromosomal origin, oriC (1), in Escherichia coli. It interacts with the RNA polymerase (2) in an early step in the initiation process (3). The dnaA protein is also involved in termination of transcription — dnaA(Ts) mutants show increased readthrough at the trp operon attenuator at nonpermissive temperature (4). The dnaA gene has been cloned (5) and the nucleotide sequence of both the promoter region and the structural gene has been determined (6, 7); the gene codes for basic polypeptide of 52.5 kD molecular weight. Transcript start sites corresponding to two promoters were found in vivo (6). Between the two promoters we found an 11 bp nucleotide sequence which is present 4 times within the minimal origin (6). These sequences are amongst those that are highly conserved within the origins of different species of Enterobacteriaceae (8). It has been suggested that the dnaA protein is regulating its own synthesis (9). To study the regulation of the dnaA gene we have fused the dnaA promoter region to the tet and lacZ genes. We found that an increased concentration of wild type dnaA protein, supplied by a second plasmid, caused repression of transcription from the dnaA promoter region.