Two genes, and encoding a prolidase and a prolidase-like protein, respectively, were cloned and characterized from subsp. bulgaricus. The identity of the and genes with the subsp. prolidase gene () was shown to be 98% and 60%, respectively. Both and were preceded by a putative promoter region. Northern analysis of mRNA revealed a 1.1 kb transcript indicating that forms a monocistronic transcriptional unit. Under the growth conditions used, no evidence was obtained that was expressed, either by mRNA size determination in Northern analysis or by primer extension analysis. With reverse transcription-PCR, however, the presence of monocistronic transcripts was established. The gene could also be overexpressed in using the vector pKK223-3. The size of the protein synthesized, 41 kDa, confirmed the molecular mass of OrfZ calculated according to DNA sequence analysis. In contrast to PepQ, which showed a substrate specificity characteristic of prolidase enzymes, no enzymic activity for the -encoded protein was found with the peptide substrates tested. These results indicate that is a cryptic gene, which is expressed at a very low level under the growth conditions used. It is noteworthy that homologues of the subsp. and genes appeared to be present in both subsp. and


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