A secreted phosphodiesterase/alkaline phosphatase, APaseD, was purified from a culture of JH646MS. Its phosphodiesterase activity was reminiscent of an APase isolated and characterized previously. Immunoassay and N-terminal sequencing showed the two proteins to be identical. Using the first 20 amino acids of the mature protein, a BLAST search of GenBank was used to find an homologous sequence. An exact match was found but in a putative non-coding region. It was hypothesized that there was a base pair deletion in the gene. A DNA fragment internal to the coding region was generated by PCR using template DNA from a strain which produced APaseD. The PCR fragment was cloned and used to interrupt the gene. Western blot analysis of the parent and the mutated strains showed that APaseD was missing in the mutant. Resequencing of the gene revealed a larger ORF encoding a protein similar in size to the 49 kDa APaseD estimated by SDS-PAGE. The promoter was then cloned, sequenced and used in promoter fusions which showed that the gene was phosphate-starvation-induced and dependent on PhoP and PhoR for expression.


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