Identification of a new regulator in Streptococcus pneumoniae linking quorum sensing to competence for genetic transformation

Competence for genetic transformation in Streptococcus pneumoniae is regula ted by a quorum-sensing system encoded by two genetic loci, comCDE and comA B. Additional competence-specific operons, cilA, cilB, cilC, cilD, cilE, ci nA-recA, coiA, and cfl involved in the DNA uptake process and recombination , share an unusual consensus sequence at -10 and -25 in the promoter, which is absent from the promoters of comAB and comCDE. This pattern suggests th at a factor regulating transcription of these transformation machinery gene s but not involved,vith comCDE and comAB expression might be an alternative sigma factor. A search for such a global transcriptional regulator was beg un by purifying pneumococcal RNA polymerase holoenzyme, In preparations fro m competent pneumococcal cultures a protein which seemed to be responsible for cilA transcription in vitro was identified, The corresponding gene tvas identified and found to be present in two copies, designated comX1 and com X2, located adjacent to two of the repeated rRNA operons, Expression of tra nsformation machinery operons, such as cilA, cilD, cilE, and cfl, but not t hat of the quorum-sensing operons comAB and comCDE, was shown to depend on comX, while comX expression depended on ComE but not on ComX itself. We con clude that the factor is a competence specific global transcription modulat or which links quorum-sensing information transduced to ComE to competence and propose that it acts as an alternate sigma factor, We also report that comAB and comCDE are not sufficient for shutoff of competence-stimulating p eptide-induced gene expression nor for the subsequent refractory period, su ggesting that these phenomena depend on one or more ComX-dependent genes.