Bacteriophage ms2 l protein: genetic and biochemical characterization

Abstract

In order to release progeny, bacteriophages must lyse the host cell by compromising the peptidoglycan layer. There are two known strategies of lysis: the holin-endolysin system and single gene lysis (SGL), which are dependent on the genome size. Large phages encode multiple proteins, including a holin and endolysin, for lysis. In contrast, small ssRNA phages (Leviviridae and Alloleviviridae) and ssDNA phages (Microviridae) do not encode a muralytic enzyme and accomplish lysis with a single gene. The cellular target of the lysis gene E from the prototypic microvirus, ?X174, and A2 from the prototypic allolevivirus, Q?, has been elucidated. In both cases, these proteins were demonstrated to inhibit specific enzymes within the peptidoglycan biosynthetic pathway and infected cells lyse as a result of septal catastrophes. The prototype Levivirus MS2 encodes L, a 75 aa polypeptide that effects lysis without inhibiting murein synthesis. The purpose of the work described in this dissertation was to characterize MS2 L using genetic and biochemical strategies. Using a genetic approach, PcnB was shown to be important to the entry of the MS2 RNA into the cytoplasm. L accumulation during infection was quantified by comparison to purified, oligohistidine-tagged L. Biochemical experiments demonstrated the L protein behaved as a periplasmic, membrane-associated protein. The morphologies of cells undergoing L-mediated lysis are significantly different from cells lysing due to A2 expression, since L-lysing cells do not show septally localized membrane protrusions.