Replication of Escherichia coli requires DNA polymerase I

Abstract

FOR many years DNA polymerase I was the only known E. coli enzyme with the ability to synthesise DNA. It was, therefore, assumed by many to be the enzyme required for DNA replication. Doubts concerning this assumption were taken seriously only when DeLucia and Cairns¹ isolated a viable E. coli mutant with less than 1% of the normal polymerase I activity in in vitro tests. The conjecture that polymerase I might not be involved at all in replication but only functions in DNA repair processes was soon superseded by the observation that polymerase I is involved in the joining of Okazaki pieces^2,3. But the question whether DNA polmerase I is essential for replication or whether it is dispensable enzyme remained open. To investigate whether DNA polymerase I is essential for replication, we attempted the isolation of conditional lethal mutations in the gene coding for polymerase I.