Transient association of an alternative sigma factor, ComX, with RNA polymerase during the period of competence for genetic transformation in Streptococcus pneumoniae

被引:106
作者
Luo, P [1 ]
Morrison, DA [1 ]
机构
[1] Univ Illinois, Dept Sci Biol, Mol Biol Lab, Chicago, IL 60607 USA
关键词
D O I
10.1128/JB.185.1.349-358.2003
中图分类号
Q93 [微生物学];
学科分类号
071005 ; 100705 ;
摘要
Natural transformation in Streptococcus pneumoiae is regulated by a quorum-sensing system that acts through accumulation and sensing of a peptide pheromone (competence-stimulating peptide [CSP]) to control many competence-specific genes acting in DNA uptake, processing, and integration. The period of competence induced by CSP lasts only 15 min (quarter-height peak width). The recently identified regulator ComX is required for the CSP-dependent expression of many competence-specific genes that share an unusual consensus sequence (TACGAATA) at their promoter regions. To test the hypothesis that this regulator acts as a transient alternative sigma factor, ComX was purified from an Escherichia coli overexpression strain and core RNA polymerase was purified from a comX-deficient S. pneumoniae strain. The reconstituted ComX-polymerase holoenzyme produced transcripts for the competence-specific genes ssbB, cinA, cglA, celA, and dalA and was inhibited by anti-ComX antibody, but not by anti-sigma(70) antibody. Western blotting using antibodies specific for CoMX, sigma(70), and poly-His revealed a transient presence of ComX for a period of 15 to 20 min after CSP treatment, while RNA polymerase remained at a constant level and sigma(A) remained between 60 and 125% of its normal level. ComX reached a molar ratio to RNA polymerase of at least 1.5. We conclude that ComX is unstable and acts as a competence-specific sigma factor.
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页码:349 / 358
页数:10
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