The angled arrows and the lollipops indicate the promoters and rh

The angled arrows and the lollipops indicate the promoters and rho-independent transcription terminators experimentally demonstrated (black) or predicted from in silico analysis (white). Sequences used for this analysis are from the putative ICE ICESpn8140 of S. pneumoniae [GenBank:FR671412[22] and from the partially or completely sequenced genomes of S. parasanguinis

ATCC15912 [GeneBank:NZ_ADVN00000000] and F0405 [GenBank:NZ_AEKM00000000], S. infantis ATCC 700779 [GeneBank:NZ_AEVD00000000] and S. australis selleck chemical ATCC700641 [GeneBank:NZ_AEQR00000000]. All these putative elements harbor selleck screening library closely related regulation modules that would be transcribed divergently from the conjugation and recombination modules. All these modules possess a similar organization and encode putative cI repressors, ImmR repressors and metalloproteases related to the ones of ICESt1/3 (64-90% protein sequence identity) and one to four unrelated proteins (Figure 6). Sequence comparison of the intergenic core regions of the closely related streptococci ICEs revealed similar regulatory signals at the same positions as in ICESt1/3 with high sequence conservation (see

additional file 2: check details S2B, S2C and S2D), suggesting a similar regulation. More distantly related conjugation modules (35-70% identity for at least seven proteins with similar organization) are found not only in previously described elements – RD2 from S. pyogenes [23] and four elements integrated in a tRNALys gene from four S. agalactiae strains [4] – but also in novel putative ICEs that we found in various Streptococci including S. agalactiae ATCC13813 (incompletely sequenced), S. dysgalactiae ATCC12394 (two elements), S. downei F0415, Streptococcus sp. 2_1_36FAA and S. gallolyticus UCN34. Only the elements found in S. dysgalactiae encode a putative cI repressor, ImmR repressor and metalloprotease. Discussion This study of ICESt1 and ICESt3, showed that their respective transcriptional organization and their mobility behaviors differ. As previously proposed from sequence analyses, all genes included in the conjugation and recombination modules of

the two elements were found to be transcriptionally linked and controlled by a single promoter. This organization allows a coordinated regulation of genes involved in conjugation and recombination, which are functionally associated during ICE transfer. For ICESt1 and ICESt3 regulation module, the cI-like encoding gene and one to two genes located downstream are expressed from the convergent promoter Parp2 or from a distal conditional promoter Parp2s. The genes encoding metalloprotease (orfQ) and cI homologs belong to a different operon expressed from another promoter PorfQ. These two operons are separated by a rho-independent transcription terminator. The ICESt1 regulation module includes two independent transcriptional units. By contrast, co-transcription of all the ORFs belonging to the regulation module was observed for ICESt3.

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