Replication at restrictive temperatures in Escherichia coli containing a polCts mutation.

Escherichia coli cells with a polCts mutation contain a temperature-sensitive DNA polymerase II and fall to replicate DNA at the restrictive temperature (43 degreees C). Mutants deficient in polymerizing activity of the other two recognized DNA polymerases in E. coli can replicate DNA. We have isolated temperature-resistant revertants from a strain containing polA-, polB-, and polCts mutations. These revertants grow at 43 degrees C, but analysis of partially purified DNA polymerase III from several such revertants shows a temperature-sensitive DNA polymerase III activity. Genetic analysis by P1 transduction confirms that such revertants can contain a polCts mutation and also a polA- mutation. We find that such revertants behave phenotypically as PolI+ cells (DNA polymerase I-containing), and extracts of such cells show a DNA polymerase I-like activity. Revertants of polA-, dnaAts and polA-, dnaBts strains do not show such a DNA polymerase activity.