Defective initiation in an Escherichia coli dnaA(Cs,Sx) mutant.

Mutations in the Escherichia coli gene for initiation of DNA replication, dnaA, which suppress the polymerization defect and growth inhibition caused by temperature-sensitive (Ts) mutations in the polymerization gene, dnaX, are called Cs,Sx. We show here that these mutations, on their own, also cause defects in initiation, including inhibition of initiation at both low (20 degrees C) and high (44 degrees C) temperatures and asynchronous initiation at both the permissive (34 degrees C) and suppression (39 degrees C) temperatures. These findings suggests a relationship between partially defective initiation and suppression of the polymerization defect, both of which occur at 39 degrees C.