A 2.6 kb DNA sequence of Streptomyces coelicolor A3(2) which functions as a transposable element

Streptomyces coelicolor A3(2) contains CCC DNA molecules, 2.6 kb in size, with an average copy number of less than one per ten chromosomes. Southern hybridisation revealed, in addition, two linear, integrated copies (A and B) of this "mini-circle" sequence per chromosome. The two integrated copies have similar (if not identical) ends and are present in the same locations in various S. coelicolor A3(2) derivatives. The mini-circle sequence is absent from S. lividans 66 and S. violaceolatus ISP5438 and from several Streptomyces species less closely related to S. coelicolor A3(2). None of a variety of Streptomyces plasmids tested contained homology to the mini-circle sequence. When a 1.8 kb fragment of the mini-circle lacking the ends of the integrated copies was inserted into KC515 (a derivative of the temperate phage phi C31 which is unable to lysogenise host strains by the natural route because the phage attachment site has been deleted) the resulting phage lysogenized S. coelicolor A3(2) (integrating into the genome of this host by homologous recombination with resident minicircle sequences) but not S. lividans or a variety of other phi C31 hosts. In contrast, a KC515 derivative (KC591) carrying the entire 2.6 kb mini-circle sequence linearized at its single BclI site (and therefore containing the integration site of the free mini-circle) lysogenized not only S. coelicolor A3(2) but also S. lividans 66 and most other strains normally lysogenized by phi C31. The KC591 lysogens of the eight Streptomyces species tested contained a linear, integrated prophage with termini apparently identical to those of the linear mini-circle copies of S. coelicolor.(ABSTRACT TRUNCATED AT 250 WORDS)