The Bacillus subtilis 168 alkaline phosphatase III gene: impact of a phoAIII mutation on total alkaline phosphatase synthesis.

The first alkaline phosphatase (APase) structural gene mutant of Bacillus subtilis 168 was constructed by using a clone identified by hybridization to a synthetic degenerative oligonucleotide. The design of the probe was based on the first 29 amino acids of the sequenced mature APase III protein, which had been isolated from the secreted fraction of vegetative, phosphate-starved cells. DNA sequencing of the clone revealed the first 80 amino acids of the APase III protein, including a typical procaryotic signal sequence of 32 amino acids preceding the start of the mature protein. The 29 amino acids encoded by the predicted open reading frame immediately following the signal sequence are identical to the first 29 amino acids of the sequenced mature protein. This region shows 80% identity to strand A of the beta sheet that is very well conserved in Escherichia coli and mammalian APases. A phoAIII structural mutant was constructed by insertional mutagenesis with a fragment internal to the coding region. The effects of this mutation on APase production in B. subtilis 168 were analyzed under both phosphate starvation and sporulation conditions. The mutation in APase III reduced the total vegetative APase specific activity by approximately 40% and sporulation APase specific activity by approximately 45%. An APase protein was isolated from sporulating cells at stage III and was identified as APase III by protein sequencing of the amino terminus and by its absence in the phoAIII mutant. The APase III gene has been mapped to approximately 50 degrees on the B. subtilis chromosome.