Nonrandom Location of Temperature-Sensitive Mutants on the Linkage Map of STREPTOMYCES COELICOLOR.

EARLIER genetic studies of Streptomyces cwlicolor utilized almost exclusively nutritional markers, and these identified two abundantly marked linkage groups (HOPWOOD 1965a). Later it was shown (HOPWOOD 1965b) that these linkage groups were segments of a circular map. The two intervening regions were very sparsely marked, and this accounted for the earlier finding of two independently segregating groups of loci. It was concluded that sparsely marked regions of the map corresponded to segments of chromosome carrying few genes accessible by a study of auxotrophs. Other classes of mutants were therefore sought in an attempt to identify loci in these regions, and to investigate the significance of a possible grouping of different classes of genes in different segments of the chromosome. 'Indispensable' temperature-sensitive mutants (HOROWITZ and LEUPOLD 1951 ) were chosen because, like some other classes of conditional lethals (ATWOOD and MUKAI 1953; CAMPBELL 1961; EPSTEIN et al. 1963), they were expected to arise in genes concerned with a wide variety of cellular processes (EDGAR and LIELAUSIS 1964).