%0 Journal Article %A Chamakura, Karthik R. %A Edwards, Garrett B. %A Young, Ry %T Mutational analysis of the MS2 lysis protein L %D 2017 %J Microbiology, %V 163 %N 7 %P 961-969 %@ 1465-2080 %R https://doi.org/10.1099/mic.0.000485 %K Escherichia coli %K lysis %K bacteriophage %I Microbiology Society, %X Small single-stranded nucleic acid phages effect lysis by expressing a single protein, the amurin, lacking muralytic enzymatic activity. Three amurins have been shown to act like ‘protein antibiotics’ by inhibiting cell-wall biosynthesis. However, the L lysis protein of the canonical ssRNA phage MS2, a 75 aa polypeptide, causes lysis by an unknown mechanism without affecting net peptidoglycan synthesis. To identify residues important for lytic function, randomly mutagenized alleles of L were generated, cloned into an inducible plasmid and the transformants were selected on agar containing the inducer. From a total of 396 clones, 67 were unique single base-pair changes that rendered L non-functional, of which 44 were missense mutants and 23 were nonsense mutants. Most of the non-functional missense alleles that accumulated in levels comparable to the wild-type allele are localized in the C-terminal half of L, clustered in and around an LS dipeptide sequence. The LS motif was used to align L genes from ssRNA phages lacking any sequence similarity to MS2 or to each other. This alignment revealed a conserved domain structure, in terms of charge, hydrophobic character and predicted helical content. None of the missense mutants affected membrane-association of L. Several of the L mutations in the central domains were highly conservative and recessive, suggesting a defect in a heterotypic protein–protein interaction, rather than in direct disruption of the bilayer structure, as had been previously proposed for L. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.000485