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Category: Bacterial Pathogenesis
Transformation and Recombination, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817992/9781555812058_Chap32-1.gif /docserver/preview/fulltext/10.1128/9781555817992/9781555812058_Chap32-2.gifAbstract:
This chapter emphasizes competence regulation and the roles of recombination and repair enzymes. More than a dozen genes encoding transformation proteins have been identified in Bacillus subtilis. Orthologs of these proteins have been recognized in other transformation systems, both gram negative and gram positive, and it appears that many aspects of the DNA uptake mechanism are conserved. The contribution of competence and sporulation factor (CSF) to modulating the expression of srfA is relatively minor, exerting only a two-to-threefold effect, but increasing the level of extracellular CSF exerts a profound inhibitory effect on srfA expression, while stimulating sporulation. Homologous recombination in B. subtilis is central to both genetic transformation in competent cells and DNA repair following exposure to agents that damage DNA. Correspondingly, many of the genes that code for recombination proteins are regulated by either ComK or the SOS DNA repair regulon; the critical recombination gene, recA, is regulated by both ComK and the SOS pathway. The current models for homologous recombination in prokaryotes are based primarily on a large body of genetic and biochemical studies in Escherichia coli. More than a dozen genes encoding recombination proteins have been identified in B. subtilis. All but two of these, recS and recU, seem to have functional counterparts in E. Coli; on the other hand, homologs of several known E. Coli recombination genes, including recE, recG, recJ, recT, and ruvC, have not been found in B. subtilis.
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Cartoon representation of DNA uptake during transformation of gram-positive and gram-negative bacteria.
Cartoon representation of DNA uptake during transformation of gram-positive and gram-negative bacteria.
The backbone pathway of competence regulation in B. subtilis.
The backbone pathway of competence regulation in B. subtilis.
The quorum-sensing system (see module 1, Fig. 2 ). (A) Genetic map of the quorum-sensing locus. The black and shaded boxes indicate the extent of the N-terminal hydrophobic and linker regions, respectively, of ComP. (B) Diagram of the quorum-sensing pathways. The box represents a cell. The circled + and — symbols indicate positive and negative effects.
The quorum-sensing system (see module 1, Fig. 2 ). (A) Genetic map of the quorum-sensing locus. The black and shaded boxes indicate the extent of the N-terminal hydrophobic and linker regions, respectively, of ComP. (B) Diagram of the quorum-sensing pathways. The box represents a cell. The circled + and — symbols indicate positive and negative effects.
Operation of the Mec switch (see module 2, Fig. 2 ). The dotted outlines indicate degradation. The circled + symbol indicates that ComK operates positively on its own promoter. A, C, P, and S represent MecA, ClpC, ClpP, and ComS, respectively.
Operation of the Mec switch (see module 2, Fig. 2 ). The dotted outlines indicate degradation. The circled + symbol indicates that ComK operates positively on its own promoter. A, C, P, and S represent MecA, ClpC, ClpP, and ComS, respectively.
Additional inputs to the backbone pathway of competence regulation (compare with Fig. 2 ). Genes above and below the backbone act positively and negatively, respectively. The quorum-sensing genes and those involved in the Mec switch are omitted from this figure. ClpP is included because it affects competence independently of its direct function in the Mec switch.
Additional inputs to the backbone pathway of competence regulation (compare with Fig. 2 ). Genes above and below the backbone act positively and negatively, respectively. The quorum-sensing genes and those involved in the Mec switch are omitted from this figure. ClpP is included because it affects competence independently of its direct function in the Mec switch.
Biochemical model for genetic recombination in Β. subtilis, adapted from reference 92 .
Biochemical model for genetic recombination in Β. subtilis, adapted from reference 92 .
Transformation genes of Bacillus subtilis
Transformation genes of Bacillus subtilis
Competence regulatory proteins of B. subtilis
Competence regulatory proteins of B. subtilis
B. subtilis recombination genes
a Organisms containing homologs with highest identity; homologs with at least 60% identity are in boldface.
B. subtilis recombination genes
a Organisms containing homologs with highest identity; homologs with at least 60% identity are in boldface.
Β. subtilis din genes
a Approximate position of center of operator sequence based on locations of putative +1. Only the recA promocer has been mapped.
b Apparent binding constants were determined by quantitative mobility shift assays ( 12 , 13 , 83 ).
c Organisms containing homologs with highest identity; homologs with at least 60% identity are in boldface.
Β. subtilis din genes
a Approximate position of center of operator sequence based on locations of putative +1. Only the recA promocer has been mapped.
b Apparent binding constants were determined by quantitative mobility shift assays ( 12 , 13 , 83 ).
c Organisms containing homologs with highest identity; homologs with at least 60% identity are in boldface.