Recombinant Enterobacteria phage lambda Host-nuclease inhibitor protein gam (gam)

Function

Both GamL and GamS bind to host RecBCD nuclease and inhibit its activities, protecting the viral DNA against RecBCD mediated degradation (PubMed:126236, PubMed:1653221, PubMed:17544443, PubMed:2943636, PubMed:4275917). Isoform GamS mimics DNA, preventing RecBCD from binding DNA (PubMed:17544443, PubMed:28009252). Expression of this protein in E.coli renders cells more sensitive to fluoroquinolone antibiotics (which inhibit topoisomerases and induce dsDNA breaks) (PubMed:28009252). Frameshift mutations that delete most of this protein (starting from position 78 or 97 of GamL) allow the bacteriophage to overcome the retron Ec48 bacteriophage defense system. Overexpression of the wild-type gam protein in E.coli with an intact Ec48 retron leads to a dramatic decrease in cell growth, the frameshift mutants do not have this effect (PubMed:33157039)

Subunit

Homodimer (PubMed:126236, PubMed:17544443, PubMed:28009252). Interacts with host RecBCD without displacing any of the subunits; this interaction prevents RecBCD from binding to DNA (PubMed:1653221, PubMed:17544443, PubMed:28009252). The GamS isoform makes extensive contacts with RecB, and inserts deeply into the RecBCD complex (PubMed:28009252)

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• Sanger F. et al. Nucleotide sequence of bacteriophage lambda DNA. — J. Mol. Biol. (1982)
• Friedman S.A. et al. Selective inhibition of Escherichia coli recBC activities by plasmid-encoded GamS function of phage lambda. — Gene (1986)
• Maruyama I.N. et al. A selective lambda phage cloning vector with automatic excision of the insert in a plasmid. — Gene (1992)
• Murphy K.C. et al. Lambda Gam protein inhibits the helicase and chi-stimulated recombination activities of Escherichia coli RecBCD enzyme. — J. Bacteriol. (1991)
• Sakaki Y. et al. Purification and properties of the gamma-protein specified by bacteriophage lambda: an inhibitor of the host RecBC recombination enzyme. — Proc. Natl. Acad. Sci. U.S.A. (1973)
• Karu A.E. et al. The gamma protein specified by bacteriophage gamma. Structure and inhibitory activity for the recBC enzyme of Escherichia coli. — J. Biol. Chem. (1975)
• Millman A. et al. Bacterial Retrons Function In Anti-Phage Defense. — Cell (2020)