Bacteriophage T4 lysis and lysis inhibition: molecular basis of an ancient story

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Title: Bacteriophage T4 lysis and lysis inhibition: molecular basis of an ancient story
Author: Tran, Tram Anh Thi
Abstract: T4 requires two proteins : holin , T (lesion formation and lysis timing ) and endolysin , E (cell wall degradation ) to lyse the host at the end of its life cycle . E is a cytoplasmic protein that sequestered away from its substrate , but the inner membrane lesion formed by T allows E to gain access to the cell wall . T4 exhibits lysis inhibition (LIN ) , a phenomenon in which a second T4 infection occurs ? 3 min after primary infection results a delay in lysis . Mutations that abolish LIN mapped to several genes but only rV encoding the holin , T , and rI , encoding the antiholin , RI , are required for LIN in all hosts which support T4 replication . Antiholin RI inhibits T -mediated lysis by direct interaction with the holin . T has at least one transmembrane domain with its Nterminus (TNTD ) in the cytoplasm and C -terminus in the periplasm (TCTD ) . In contrast , the N -terminus of RI (RINTD ) is predicted to function as a cleavable signal sequence allowing the secretion of the RI C -terminal domain (RICTD ) into the periplasm . Most of RI mutations which abolish LIN occur in the RICTD , suggesting RI inhibits T -mediated lysis by interacting with T via RICTD . Topological analysis of RI and T showed that fusion of PhoA signal sequence (ssPhoA ) to RICTD is necessary and sufficient for LIN and ssPhoA ?TCTD interferes with RI -mediated LIN , indicating T and RI interact via periplasmic C -terminal domains . In T4 infection , LIN is observed only when superinfection takes place , indicating either the antiholin or the LIN signal must be unstable . Both RI and RINTD ?PhoA are localized to both the inner membrane and the periplasm suggesting that the RINTD is a Signal -Anchor -Release (SAR ) domain . Protein stability studies indicated that the SAR domain is the proteolytic determinant of RI , and DegP is the protease that is responsible for RI degradation . To date , how TNTD participates in lysis and LIN is not known . Modifications and deletion of the N -terminus of T change the lysis time , indicating this domain is involved the in timing of lysis . GFP fusion to holin T allowed microscopic visualization of fluorescent patches on the membrane at the time of lysis .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1241
Date: 2009-05-15

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Bacteriophage T4 lysis and lysis inhibition: molecular basis of an ancient story. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1241 .

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