Phosphotransferase system of Streptococcus salivarius: characterization of the ptsH gene and its product

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The Streptococcus salivarius ptsH gene encoding histidine-containing phosphocarrier protein (HPr) of the phosphotransferase system (PTS) has been cloned, sequenced, and found to be part of a ptsH, ptsI operon. Upstream from ptsH, putative −35 and −10 boxes and a Shine-Dalgarno sequence highly similar to the Escherichia coli consensus regulatory elements were identified. A second promoter, located in the ptsH coding sequence was also observed and is sufficient for the expression of the S. salivarius ptsI gene, encoding enzyme I of the PTS in E. coli [Gagnon et al., Gene 121 (1992) 71–78]. The amino acid sequence of S. salivarius HPr, inferred from the ptsH sequence, shared identity varying between 37 and 76% with known HPr from other bacteria. Moreover, the S. salivarius HPr shared 78% identity with an HPr-like protein of Aspergillus fumigatus, a eukaryotic mold that does not possess a functional PTS. Expression analysis of S. salivarius HPr in E. coli demonstrated that ( i) S. salivarius ptsH is expressed in E. coli under the control of its own promoter, (ii) S. salivarius HPr synthesized by E. coli is completely processed by methionine aminopeptidase, and ( iii) S. salivarius HPr is phosphorylated in vivo by E. coli enzyme I. It was also observed that, in E. coli, the copy number of pUC18 bearing S. salivarius ptsH was reduced more than 25-fold, as compared to pUC18 without an insertion.