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 assigned to the genus Streptomyces on the basis of distinctive morphological features. A genomic library of A21 DNA has been constructed and transformed into Escherichia coli K-12 using a high-copy-number vector. One of the recombi- nant plasmids activates the cryptic bgl operon when in- serted into appropriate strains. The complete sequence of the 1629-bp A21 DNA fragment has been deter- mined. The analysis revealed the presence of an ORF whose putative product shows a high degree of similarity to RNA polymerase sigma factors; we therefore desig- nated the gene psfS (Putative sigma factor, Strepto- myces). Mapping of the 5¢ terminus of transcript by primer extension indicated that PsfS induces transcrip- tion initiation within the bgl promoter-silencer region.