Protein secretion in Streptomyces griseus N2-3-11: characterization of the secA gene and its growth phase-dependent expression.

The chromosomal region encoding the secA gene of Streptomyces griseus N2-3-11 was cloned and analyzed. The secA gene encodes a polypeptide of 939 aa with a molecular mass of 105 kDa. The growth defect of temperature sensitive Escherichia coli secA mutants was not restored by the S. griseus SecA. The secA promoter was analyzed and the transcriptional start point of the gene was determined. Northern blot and Western blot analyses revealed a growth phase dependent secA expression. The integration of an additional copy of the S. griseus secA gene into the genome of S. lividans TK23 had no visible effect on the efficiency of protein secretion.