CLONING AND SEQUENCING OF A SECY HOMOLOG FROM STREPTOMYCES-SCABIES

The complete DNA sequence of the Streptomyces scabies (Ss) secY homolo g and partial sequences of adjacent upstream and downstream open readi ng frames (ORFs) have been determined. The nucleotide sequence of a 2- kb region predicts a polypeptide of 437 amino acids in length with hom ology to the SecY protein family. The Ss secY homolog lies upstream fr om a sequence that has homology to the adenylate kinase gene (adk) fam ily. The translational stop codon of the putative SecY ORF overlaps th e predicted start codon for the Adk ORF. Another ORF that lies upstrea m from the secY homolog has sequence similarity to the genes that code for the L15 r-protein. Within the 243-bp intergenic region between th e L15 and SecY coding sequences, the presence of a streptomycete-like promoter sequence and an 18-bp inverted repeat suggests that the secY homolog and the adjacent downstream sequences may be transcribed indep endently of the L15 coding sequence. Transcript analysis indicates tha t the secY homolog is expressed in both Ss and Streptomyces lividans. The proposed gene and transcript organization of the L15-SecY-Adk codi ng regions in the Ss clone resembles that of Micrococcus luteus which, like the streptomycetes, has a G+C-rich genome.