The Chromosome Map ofStreptomyces coelicolorA3(2)

Genetic mapping of the chromosome of Streptomyces coelicolor A3(2) began with the analysis of haploid recombinants selected from matings. A physical map of the S. coelicolor chromosome has recently been constructed, using pulsed-field gel electrophoresis of AseI and DraI fragments. The genetic map was found to be reasonably congruent with the physical map over the well-marked quadrants. It was also apparent that the silent regions are indeed long stretches of DNA. It certainly appears at present that wild-type streptomycetes carry considerable stretches of DNA that presumably has selective value in natural habitats-otherwise it would not have persisted-but has only subtle effects on phenotype when deleted in laboratory variants. The arrangement of genes in the well-marked segments seems to be extensively conserved even between streptomycetes that are not very closely related, as in the well-known case of E. coli K-12 and S. typhimurium LT2, or in pseudomonads, which show extensive map similarities for groups of genes of primary metabolism but not for segments determining specialized functions peculiar to individual species.