A putative sigma factor from Streptomyces sp. strain A21 can activate the expression of the cryptic operon bgl in Escherichia coli K-12

Streptomyces sp A21 is a cellulolytic strain isolated from soil which was a ssigned to the genus Streptomyces on the basis of distinctive morphological features. A genomic library of A21 DNA has been constructed and transforme d into Escherichia coli K-12 using a high-copy-number vector. One of the re combinant plasmids activates the cryptic bgl operon when inserted into appr opriate strains. The complete sequence of the 1629-bp A21 DNA fragment has been determined. The analysis revealed the presence of an ORF whose putativ e product shows a high degree of similarity to RNA polymerase sigma factors ; we therefore designated the gene psfS ((P) under bar utative (s) under ba r igma (f) under bar actor, (S) under bar treptomyces). Mapping of the 5' t erminus of transcript by primer extension indicated that PsfS induces trans cription initiation within the bgl promoter-silencer region.