Published online by Cambridge University Press: 14 April 2009
Initial experiments demonstrated that the plasmid R6K cannot be transferred to or maintained readily in the E. coli DNA polymerase I deficient strain JG138 polA1. Results with E. coli MM386 polA12 (R6K), which has a temperature sensitive polymerase I enzyme, showed cell division becomes abnormal when the polymerase I enzyme of the host bacteria is inactivated at the restrictive temperature. Under conditions of polymerase I deficiency, R6K replication, as measured by monitoring R-factor-mediated β-lactamase activity, also becomes abnormal with the loss of multiple R6K copies per cell and the apparent maintenance of a single R-factor copy per cell.