Characterization of the secA gene of Streptomyces lividans encoding a protein translocase which complements and Escherichia coli mutant defective in the ATPase activity of SecA

The secA gene of Streptomyces lividans was cloned using as probe a 57-mer oligonucleotide based on conserved sequences of the Escherichia coli secA and the Bacillus subtilis div genes. It encodes a protein of 946 amino acids (aa) with a deduced M(r) of 106,079, with high similarity to all known SecA proteins. All the previously described conserved motifs of SecA proteins were conserved in the S. lividans protein. The secA gene of S. lividans restored sensitivity to sodium azide in E. coli SecA4 (AzR) a mutant with an azide-resistant (ATPase defective) SecA protein. However, it did not complement the temperature-sensitive mutation in E. coli MM52 (SecAts) (a conditional lethal mutant defective in protein translocation) allowing only poor growth at the nonpermissive temperature. secA homologous sequences were present in 11 different species of Streptomyces and Nocardia.