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Updated: May 26, 2025

Phage Phenomics: Physiological Approaches to Characterize Novel Viral Proteins
Published on: June 11, 2015
Phage parasites targeting phage homologous recombinases provide antiviral immunity
Gianluca Debiasi-Anders1,2, Cuncun Qiao1,2, Amrita Salim1,2
1Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden.
Abstract:
Bacteria often carry multiple genes encoding anti-phage defense systems, clustered in defense islands and phage satellites. Various unrelated anti-phage defense systems target phage-encoded homologous recombinases (HRs) through unclear mechanisms. Here, we show that the phage satellite SaPI2, which does not encode orthodox anti-phage defense systems, provides antiviral immunity mediated by Stl2, the SaPI2-encoded transcriptional repressor. Stl2 targets and inhibits phage-encoded HRs, including Sak and Sak4, two HRs from the Rad52-like and Rad51-like superfamilies. Remarkably, apo Stl2 forms a collar of dimers oligomerizing as closed rings and as filaments, mimicking the quaternary structure of its targets. Stl2 decorates both Sak rings and Sak4 filaments. The oligomerization of Stl2 as a collar of dimers is necessary for its inhibitory activity both in vitro and in vivo. Our results shed light on the mechanisms underlying antiviral immunity against phages carrying divergent HRs.
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