| dc.description |
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 , φX174 , and A2 from the prototypic allolevivirus , Qβ , 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 . |
|