Fig. 4
Modification of the csRNA3 sequence by prophage insertion. A Modification of ccnC through insertion of Ï•OXC141 into attBOXC. The insertion of Ï•OXC141, indicated by the pink genes integrated downstream of purA, into the S. pneumoniae OXC141 genome is compared to the unmodified attBOXC site of R6 using BLASTN. The red bands link regions of similar sequence, with the colour indicating the level of sequence identity between the pair. The black vertical lines show how the cellular ccnC gene at the attB site is split into the ccnCL and ccnCR genes at the attL and attR sites, respectively. B Model of csRNA3 and csRNA3L-mediated inhibition of competence. Pneumococcal competence is regulated by a quorum-sensing mechanism. The comC gene encodes a pre-peptide that is exported and processed into competence-stimulating peptide (CSP) by the ComAB transporter. CSP is detected by the ComDE two competent system, which activates the transcription of early competence genes such as comX. The ComX alternative sigma factor then drives expression of the late competence genes required for uptake of DNA from the environment. The csRNA3 RNA inhibits the production of CSP by either blocking translation of the comC gene, or triggering degradation of the comC transcript. By reducing the autoinduction of the comCDE operon, the csRNA molecule suppresses further comC transcription. This delays or prevents the induction of competence by endogenously produced CSP, but does not affect the induction of competence by exogenously supplied CSP. This inhibition is affected by the interconversion between csRNA3P (encoded by ccnCP at attP) and csRNA3 (encoded by ccnC at attB), when a phage is excised from the chromosome, and csRNA3L (encoded by ccnCL at attL) and csRNA3R (encoded by ccnCR at attR), when the prophage is integrated. The enhanced activity of csRNA3L, represented by the thicker line indicating inhibition of comC expression, should therefore further delay or inhibit the spontaneous induction of the competence machinery, without affecting cell responses to CSP added in vitro