Consequences of modification on the association of DNA polymerase with the cell membrane

1. This is a report of a possible causal relation between the structure of the membrane-bound DNA polymerase and the mutator characteristic of Exherichia coli, mut T1. The characteristics of the membrane-bound polymerase are compatible with its identification as DNA polymerase II, and enzyme which has been determined to be genetically closely linked to the mut T1 gene. Several genes concerned with membrane structure are also known to be linked to the mutator locus. 2. Differences exist between membrane-bound polymerase activity of a wild-type E. coli K-12 and of an isogenic strain harboring the mutator gene. (a) The cell membranes of the mutator strain retain 5--6 times as much activity as do membrane complexes from wild-type cells. (b) The DNA polymerase activity of the membranes from the mut T1 strain is less sensitive to inhibition by the sulfhydryl-binding reagent, N-ethylmaleimide. (c) The membrane-DNA polymerase complex of mut T1 cells uses endogenous, membrane-bound DNA for replication-repair in preference to exogenous DNA. 3. The differences described are specific to structural differences in the membrane complex. When DNA polymerase activity is solubilized from the complexes, the enzymes of the two strains exhibit similar characteristics. These results are consistent with the thesis that an alteration in membrane structure is the basis of mut T1 activity. The results do not support any hypothesis that mut T1 phenotype is a reflection of mutations in the structural gene for DNA replicase (polymerase) or its components.