Regulation of transfer functions by the imp locus of the Streptomyces coelicolor plasmidogenic element SLP1

SLP1(int) is a 17.2-kb genetic element that normally is integrated site spe cifically into the chromosome of Streptomyces coelicolor A3(2). The imp ope ron within SLP1(int) represses replication of both chromosomally integrated and extrachromosomal SLP1. During mating with S. lividans, SLP1(int) can e xcise, delete part of imp, and form a family of autonomously replicating co njugative plasmids. Earlier work has shown that impA and impC gene products act in concert to control plasmid maintenance and regulate their own trans cription. Here we report that these imp genes act also on a second promoter , P-opimp (promoter opposite imp), located adjacent to, and initiating tran scription divergent from, imp to regulate loci involved in the intramycelia l transfer of SLP1 plasmids. spdB1 and spdB2, two overlapping genes immedia tely 3' to P-opimp and directly regulated by imp, are shown by Tn5 mutagene sis to control transfer-associated growth inhibition (i.e., pocking). Addit ional genes resembling transfer genes of other Streptomyces spp. plasmids a nd required for SLP1 transfer and/or post-conjugal intramycelial spread are located more distally to P-opimp. Expression of impA and impC in an otherw ise competent recipient strain prevented SLP1-mediated gene transfer of chr omosomal and plasmid genes but not plasmid-independent chromosome-mobilizin g 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 r eported here implicate imp in the overall regulation of functions related t o the extrachromosomal state of SLP1.