Diversity and strength of internal outward-oriented promoters in group IIC-attC introns.
Integrons are genetic elements that incorporate mobile gene cassettes by site-specific recombination and express them as an operon from a promoter (Pc) located upstream of the cassette insertion site. Most gene cassettes found in integrons contain only one gene followed by an attC recombination site. We have recently shown that a specific lineage of group IIC introns, named group IIC-attC introns, inserts into the bottom strand sequence of attC sites. Here, we show that S.ma.I2, a group IIC-attC intron inserted in an integron cassette array of Serratia marcescens, impedes transcription from Pc while allowing expression of the following antibiotic resistance cassette using an internal outward-oriented promoter (P(out)). Bioinformatic analyses indicate that one or two putative P(out), which have sequence similarities with the Escherichia coli consensus promoters, are conserved in most group IIC-attC intron sequences. We show that P(out) with different versions of the -35 and -10 sequences are functionally active in expressing a promoterless chloramphenicol acetyltransferase (cat) reporter gene in E. coli. P(out) in group IIC-attC introns may therefore play a role in the expression of one or more gene cassettes whose transcription from Pc would otherwise be impeded by insertion of the intron.
Léon
Grégory
G
Centre de Recherche en Infectiologie, Centre Hospitalier Universitaire de Québec, Québec, Canada.
Quiroga
Cecilia
C
Centrón
Daniela
D
Roy
Paul H
PH
D001483:Base Sequence; D015500:Chloramphenicol O-Acetyltransferase / Q000032:analysis; D019295:Computational Biology; D005798:Genes, Bacterial; D017930:Genes, Reporter; D032023:Integrons; D007438:Introns; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012706:Serratia marcescens / Q000235:genetics; D024363:Transcription Initiation Site; D014158:Transcription, Genetic
D015500:Chloramphenicol O-Acetyltransferase