CLONING AND CHARACTERIZATION OF A GENE ENCODING A SECRETED TRIPEPTIDYL AMINOPEPTIDASE FROM STREPTOMYCES-LIVIDANS-66

The gene encoding a tripeptidyl aminopeptidase (Tap) from Streptomyces lividans was cloned by using a simple agar plate activity assay. Over expression of the cloned gene results in the production of a secreted protein,which has an apparent subunit molecular weight of 55,000 and i s responsible for the major aminoterminal degradative activity in cult ure broths of S. lividans strains, A DNA sequence analysis revealed a potential protein-encoding region of the size expected to encode the o bserved protein, which contained a sequence that exhibited significant homology around a putative active site serine residue observed far li pases, esterases, and acyl transferases. Preceding the amino terminus of the secreted protein was a predicted signal peptide of 36 amino aci ds followed by a tripeptide, which could be autocatalytically removed from a secreted Tap precursor, The transcriptional start site for the gene was mapped by primer extension. Mutant strains of S. lividans lac king detectable Tap activity were able to grow and sporulate normally. Cross-species hybridization experiments showed that DNA homologs of t he fap gene are present in most of the Streptomyces strains tested.