THE CHROMOSOMAL DNA OF STREPTOMYCES-LIVIDANS 66 IS LINEAR

Two copies of a DNA sequence similar or identical to one end of the li near plasmid SLP2 were found on the Streptomyces lividans chromosome. Restriction mapping showed that these sequences represented free ends. Electrophoretic retardation and glass-binding studies indicated that the telomeres carry covalently bound proteins. Moreover, the chromosom e migrated as an 8 Mb linear DNA in pulsed-field gel electrophoresis. A similar finding with the chromosomes of six other Streptomyces speci es suggested that a linear chromosome may be characteristic of the gen us. The S. lividans chromosome can be circularized by joining the two ends by artificial targeted recombination or by spontaneous deletions spanning both telomeres. Thus the chromosome appears to be able to exi st, in viable bacteria, as a linear or a circular molecule.