Streptomyces temperate bacteriophage integration systems for stable genetic engineering of actinomycetes (and other organisms)

I center dot C31, I center dot BT1, R4, and TG1 are temperate bacteriophages with broad host specificity for species of the genus Streptomyces. They form lysogens by integrating site-specifically into diverse attB sites located within individual structural genes that map to the conserved core region of streptomycete linear chromosomes. The target genes containing the I center dot C31, I center dot BT1, R4, and TG1 attB sites encode a pirin-like protein, an integral membrane protein, an acyl-CoA synthetase, and an aminotransferase, respectively. These genes are highly conserved within the genus Streptomyces, and somewhat conserved within other actinomycetes. In each case, integration is mediated by a large serine recombinase that catalyzes unidirectional recombination between the bacteriophage attP and chromosomal attB sites. The unidirectional nature of the integration mechanism has been exploited in genetic engineering to produce stable recombinants of streptomycetes, other actinomycetes, eucaryotes, and archaea. The I center dot C31 attachment/integration (Att/Int) system has been the most widely used, and it has been coupled with the I center dot BT1 Att/Int system to facilitate combinatorial biosynthesis of novel lipopeptide antibiotics in Streptomyces fradiae.