Mutational Biosynthesis of Novel Rapamycins by a Strain of Streptomyces hygroscopicus NRRL 5491 Disrupted in rapL, Encoding a Putative Lysine Cyclodeaminase

The gene rapL lies within the region of the Streptomyces hygroscopicus chromosome which contains the biosynthetic gene cluster for the immunosuppressant rapamycin. Introduction of a frameshift mutation into rapL by ΦC31 phage-mediated gene replacement gave rise to a mutant which did not produce significant amounts of rapamycin. Growth of this rapL mutant on media containing added l-pipecolate restored wild-type levels of rapamycin production, consistent with a proposal that rapL encodes a specific l-lysine cyclodeaminase important for the production of the l-pipecolate precursor. In the presence of added proline derivatives, rapL mutants synthesized novel rapamycin analogs, indicating a relaxed substrate specificity for the enzyme catalyzing pipecolate incorporation into the macrocycle.