Formation and stability of the bacteriophage lambda replication complexes in UV-irradiated Escherichia coli

Bacteriophage lambda replication complex, containing the phage-encoded O in itiator protein protected from proteases by other elements of this complex, is a stable structure that can be inherited by one of the two daughter lam bda DNA copies after a replication round in Escherichia coli. In normal gro wth conditions in bacteria bearing a plasmid derived from bacteriophage lam bda, such a complex may be stable for many cell generations. However, it wa s found that this stable structure is disassembled under certain conditions , namely, after heat shock. Therefore, we asked whether other environmental stresses may cause disassembly of the lambda replication complex. We found that UV irradiation of the host cells prevented formation of the stable la mbda replication complex (though not preventing phage replication), while t he same UV doses did not affect the stability of the replication complex as sembled prior to the irradiation. These results indicate that the stable la mbda replication complex, although sensitive to heat shock, is resistant to some other environmental stresses and that formation of at least two types of lambda replication complexes is possible. Both stable and unstable lamb da replication complexes are functional because replication of lambda DNA u nder conditions preventing formation of the stable complex proceeds efficie ntly.