dnaA acts before dnaC in the initiation of DNA replication

We constructed a double mutant of Escherichia coli K-12 carrying dnaA(Ts) and dnaC(Cs) lesions. In this mutant DNA synthesis proeceeds normally at 32 degrees C and initiation is inhibited at both 41 and 20 degrees C. By shifting this culture grown at 32 degrees C to the two restrictive temperatures in different time sequences and assaying protein and DNA synthesis of cells growing at different temperatures, we found that dnaA and dnaC genes work independently with dnaA acting before dnaC. While preparing special strains for this work, we also showed that the order of genes in the neighborhood of dnaA is dnaA-tnaA-phoS-ilv.