1. Model of the transcriptional organization of the S
Model of the transcriptional organization of the S. mutans response to CSP in peptide-rich medium.
Model of the transcriptional organization of the S. mutans response to CSP in peptide-rich medium. In step 1, extracellular CSP activates the two-component system ComED, which then induces the expression of four operons comprising several bacteriocin and bacteriocin immunity genes. The bacteriocins are suggested to create pores in the membrane that allow the entrance of the XIP pheromone into the cells. In step 2, XIP binds to ComR, which then assumes a conformation that activates the expression of two operons, one initiated at comS, creating a positive feedback loop, and the other initiated at sigX, activating the competence response. In step 3, SigX activates the expression of 22 operons, including 4 sense transcripts that are not seen in other streptococcal transcriptomes (noncore), 3 transcripts in the antisense direction (not yet investigated in other streptococci), and 15 operons encoding genes that are in the core of the streptococcal SigX response. Three groups of core genes were identified: (i) core orthologs found in at least four of the available transcriptomes, (ii) core orthologs found only in strains that belong to the DpnII group of restriction-modification systems, and (iii) core nonorthologs that have in common a conserved domain associated with similar functions (in this class are CbpD of S. pneumoniae and S. thermophilus and LytF of S. mutans, S. gordonii, and S. sanguinis, both of which have the lytic CHAP domain in common).
R. Khan et al. mSystems 2016; doi: /mSystems