What makes the lysis clock tick? A study of the bacteriophage holin

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Title: What makes the lysis clock tick? A study of the bacteriophage holin
Author: White, Rebecca Lynn
Abstract: The timing of host lysis is the only decision made in the bacteriophage lytic cycle . To optimize timing , double -stranded DNA phages use a 2 -component lysis system consisting of a muralytic enzyme , the endolysin , and a small membrane protein , the holin , which controls the timing of lysis . The best characterized holin gene to date is the S gene of bacteriophage ? . One unusual feature of the S gene is that it produces two proteins of opposing function : the holin , S105 , and the antiholin , S107 . Raab et al isolated and characterized a number of S mutants , but all of them expressed both the holin and the antiholin ; it is possible , then , that the true extent of the holin -holin interactions were masked by interactions with the antiholin . Thus , a large number of S105 mutants were created , and their phenotypes characterized in the absence of the antiholin . The interaction between those mutants and the wild -type were examined in an attempt to better understand what determines the timing of hole formation by S105 . S105 and S107 differ only by two amino acids at the N -terminus ; S107 has an additional Met -Lys sequence . Previous studies have shown that S107 may have a different topology to S105 , where the N -terminus of S107 is located in the cytoplasm and is cannot flip through the membrane because of the extra cationic side chain . This study investigates the role of the N -terminal transmembrane domain of the S proteins in terms of hole formation and its role in the antiholin character of S107 . Previous results suggest that S105 forms hole via a large oligomeric structure termed the ?death raft ? . The death raft model states that after S105 is inserted into the membrane , it forms ?rafts ? , which grow in size until a spontaneous channel forms leading to depolarization of the membrane and hole formation . This study investigates the pathway of hole formation at the single -cell level , using a C -terminal fusion of S105 and green fluorescent protein , and attempts to address several of the predictions posed by the death raft model .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2766
Date: 2009-05-15


What makes the lysis clock tick? A study of the bacteriophage holin. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2766 .

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