engleski

A second OTC-gene cluster in Streptomyces rimosus?

S. rimosus, the OTC producer, has been characterised genetically and physically. The OTC-cluster was cloned1 and its sequencing has been almost completed. A physical map of the 8 Mb linear chromosome shows that it lies in a 'genetically-silent' region, about 600 kb from one chromosome end, which might account for its frequent spontaneous amplification and deletion3. Class II mutants deleted one chromosomal end including the whole cloned OTC-cluster2. However, variants of the Class II mutants that had regained the antibiotic activity were isolated ('Class IIR'). The compound made by these Class IIR variants was identified as OTC. More detailed investigation of the progenitor Class II mutants revealed that they also synthesize an extremely small amount of OTC as identified by both TLC and HPLC. The chromosomal DNA of these new Class IIR isolates showed hybridization with some of the cloned otc genes but not with others. This observation was extended by pulsed-field gel electrophoresis (PFGE) analysis which showed that Class IIR variants had different AseI banding patterns to Class II, or to the parent strain. The otc-probes hybridized with new fragments on the PFGE gel that are bigger in size than the band which hybridizes well in the wild type. 1. Butler, M.J., C. Binnie, I.S. Hunter, D.A. Sudgen & M. Warren. Dev. Ind. Microbiol., 31, 41-50, 1990. 2. Gravius, B., T. Bezmalinović, D. Hranueli & J. Cullum. Appl. Environ. Microbiol., 59, 2220-2228, 1993. 3. Pandza, K., G. Pfalzer, J. Cullum & D. Hranueli. Microbiol., 1997 (in press).

Streptomyces rimosus; oxytetracycline; deletion

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