A Conserved Phage Recombinant System Counters Host CRISPR Immunity

The discovery of CRISPR-Cas systems and their antagonistic anti-CRISPR proteins (Acrs) exemplifies the perpetual arms race between bacteria and phages. While bacterial CRISPR-Cas systems function as adaptive immune mechanisms to combat phage infection, phages have evolved counterstrategies, such as various Acrs that disrupt CRISPR-mediated immunity via diverse molecular pathways. Here, we report the identification of a phage-encoded multi-protein system conferring anti-type I-F CRISPR activity. This system consists of three functionally distinct proteins: a RecA ATPase (SSAP), a DUF669 domain-containing protein (SSB), and a RecB exonuclease (Exo). Our mechanistic analysis reveals that SSB acts as a first-response mediator, forming a polymeric assembly to specifically binding to the Csy_dsDNA R-LOOP structure. This interaction creates a molecular platform enabling the coordinated recruitment of SSAP and Exo, which collectively execute homologous recombination-mediated repair of CRISPR-induced phage DNA break. These findings establish a paradigm of multi-protein synergy in phage counter-defense strategies, advancing our understanding of the intricate evolutionary dynamics in host-phage conflicts.