An ssRNA Phage Single-gene Lysis Protein Targeting MraY Reveals Convergent Evolution Across the RNA-DNA Phage Boundary

Sgl protein from the ssRNA phage varphiCb5 targets MraY, and its membrane topology and residue distribution parallel the varphiX174 E protein despite no detectable sequence similarity.

• Why it matters: Host lysis by single Sgl proteins can block peptidoglycan synthesis at distinct steps, but how an ssRNA phage Sgl can inhibit MraY—and whether this reflects convergence or crossover—was unknown.
• What they did: Physiological evidence was used to show Sgl< varphiCb5 inhibits MraY; the study compared hydrophobic/charged residue distribution and an N-out, C-in topology, and tested lytic activity in an Sgl< varphiCb5>-LacZ fusion.
• The result: Expression of the Caulobacter FKBP-type isomerase CC2799 enhances Sgl< varphiCb5–mediated lysis in E. coli, supporting functional parallels across the RNA–DNA phage boundary.

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