The origin of replication, oriC, and the dnaA protein are dispensable in stable DNA replication (sdrA) mutants of Escherichia coli K-12.

The sdrA224 mutants of Escherichia coli K-12, capable of continued DNA replication in the absence of protein synthesis (stable DNA replication), tolerate inactivation of the dnaA gene by insertion of transposon Tn10. Furthermore, oriC, the origin of E. coli chromosome replication, can be deleted from the chromosome of sdrA mutants without loss of viability. The results suggest the presence of a second, normally repressed, initiation system for chromosome replication alternative to the 'normal' dnaA+ oriC+-dependent initiation mechanism.