Plays a role in the inhibition of the host RecBCD complex (also called exonuclease V) (Probable). A double mutation in this protein and the nucleotide kinase gp1.7 protein allows phage to overcome the retron Ec48 bacteriophage defense system. Overexpression of the wild-type gp5.9 protein in E.coli with an intact Ec48 retron leads to a dramatic decrease in cell counts consistent with cell death, the L23P mutant does not have this effect (PubMed:33157039). In (PubMed:127051), the authors do not clearly identify gene 5.9 protein but a T7 protein as having this activity. Later publications assign this activity to gene 5.9 protein.