DECREASE IN THE LINKING NUMBER OF PLASMID DNA IN DNAA MUTANTS OF ESCHERICHIA-COLI

We made use of agarose gel electrophoresis in the presence of chloroqu ine to examine the linking number of plasmids in temperature-sensitive dnaA mutants, including dnaA5 and dnaA46 mutants. The linking number of DNA prepared from dnaA mutants growing at 37 degrees C was lower th an that from wild type cells yet there was no significant difference w hen cells were grown at 28 degrees C. Complementation analysis with a plasmid containing the wild type dnaA gene and phage p1-mediated trans duction confirmed that mutations in the dnaA gene were responsible for the decrease in the linking number of DNA. (C) 1996 Academic Press