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Transcriptional Profiling of Colicin-Induced Cell Death of Escherichia coli MG1655 Identifies Potential Mechanisms by Which Bacteriocins Promote Bacterial Diversity. Daniel Walker, 2004.We report the transcriptional response of Escherichia coli MG1655 to damage induced by colicins E3 and E9, bacteriocins that kill cells through inactivation of the ribosome and degradation of chromosomal DNA, respectively . Colicin E9 strongly induced the LexA-regulated SOS response, while colicin E3 elicited a broad response that included the induction of cold shock genes, symptomatic of translational arrest . Colicin E3 also increased the transcription of cryptic prophage genes and other laterally acquired mobile elements . The transcriptional responses to both these toxins suggest mechanisms that may promote genetic diversity in E . coli populations, pointing to a more general role for colicins in adaptive bacterial physiology than has hitherto been realized . Peptidoglycan Synthesis in the Absence of Class A Penicillin-Binding Proteins in Bacillus subtilis. Derrell C. McPherson, 2003.Penicillin-binding proteins (PBPs) catalyze the final, essential reactions of peptidoglycan synthesis . Three classes of PBPs catalyze either trans-, endo-, or carboxypeptidase activities on the peptidoglycan peptide side chains . Only the class A high-molecular-weight PBPs have clearly demonstrated glycosyltransferase activities that polymerize the glycan strands, and in some species these proteins have been shown to be essential . The Bacillus subtilis genome sequence contains four genes encoding class A PBPs and no other genes with similarity to their glycosyltransferase domain . A strain lacking all four class A PBPs has been constructed and produces a peptidoglycan wall with only small structural differences from that of the wild type . The growth rate of the quadruple mutant is much lower than those of strains lacking only three of the class A PBPs, and increases in cell length and frequencies of wall abnormalities were noticeable . The viability and wall production of the quadruple-mutant strain indicate that a novel enzyme can perform the glycosyltransferase activity required for peptidoglycan synthesis . This activity was demonstrated in vitro and shown to be sensitive to the glycosyltransferase inhibitor moenomycin . In contrast, the quadruple-mutant strain was resistant to moenomycin in vivo . Exposure of the wild-type strain to moenomycin resulted in production of a phenotype similar to that of the quadruple mutant .
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