Regulation of Transfer Functions by theimp Locus of the Streptomyces coelicolorPlasmidogenic Element SLP1

ABSTRACT SLP1int is a 17.2-kb genetic element that normally is integrated site specifically into the chromosome ofStreptomyces coelicolor A3(2). The imp operon within SLP1int represses replication of both chromosomally integrated and extrachromosomal SLP1. During mating withS. lividans, SLP1int can excise, delete part of imp, and form a family of autonomously replicating conjugative plasmids. Earlier work has shown thatimpA and impC gene products act in concert to control plasmid maintenance and regulate their own transcription. Here we report that these imp genes act also on a second promoter, Popimp (promoter oppositeimp), located adjacent to, and initiating transcription divergent from, imp to regulate loci involved in the intramycelial transfer of SLP1 plasmids. spdB1 andspdB2, two overlapping genes immediately 3′ to Popimp and directly regulated byimp, are shown by Tn5 mutagenesis to control transfer-associated growth inhibition (i.e., pocking). Additional genes resembling transfer genes of other Streptomyces spp. plasmids and required for SLP1 transfer and/or postconjugal intramycelial spread are located more distally to Popimp. Expression of impA andimpC in an otherwise competent recipient strain prevented SLP1-mediated gene transfer of chromosomal and plasmid genes but not plasmid-independent chromosome-mobilizing activity, suggesting that information transduced to recipients after the formation of mating pairs affects imp activity. Taken together with earlier evidence that the imp operon regulates SLP1 DNA replication, the results reported here implicate imp in the overall regulation of functions related to the extrachromosomal state of SLP1.