In Vivo Studies on the Interaction of RecBCD Enzyme and Lambda Gam Protein

The interaction between the RecBCD enzyme of Escherichia coli and the lambda Gam protein was investigated. Two types of experiments were done. In one type, Gam protein was produced by transient induction of the cells lysogenic for lambda cI857gam+. The presence of Gam protein, which inhibits RecBCD nuclease, enabled these cells to support the growth of a gene 2 mutant of bacteriophage T4 (T4 2). The lysogens overproducing the RecB subunit of RecBCD enzyme could titrate Gam protein and thus prevent the growth of T4 2. In contrast, the lysogens overproducing either RecC or RecD retained their capacity for growth of T4 2. It is therefore concluded that the RecB subunit is capable of binding Gam protein. In the second type of experiments, Gam protein was provided by derepressing the gamS gene on the plasmid pSF117 (S. A. Friedman and J. B. Hays, Gene 43:255-263, 1986). The presence of this protein did not interfere with the growth of wild-type cells (which were F-). Gam protein had a certain effect on recF mutants, whose doubling time became significantly longer. This suggests that the recF gene product plays an important role in maintenance of viability of the Gam-expressing cells. Gam protein exerted the most striking effect on growth of Hfr bacteria. In its presence, Hfr bacteria grew extremely slowly, but their ability to transfer DNA to recipient cells was not affected. We showed that the effect on growth of Hfr resulted from the interaction between the RecBCD-Gam complex and the integrated F plasmid.