Summary: Cells of strain Challis were incubated with sodium lauroylsarcosinate to extract surface proteins. A polypeptide of apparent molecular mass 16 kDa comprising about 12% of the extract was purified using anion-exchange chromatography. The polypeptide was shown to be a phosphocarrier protein (HPr) that could also be found in the soluble (cytoplasmic) fraction from cells broken by homogenization with glass beads. labelling of cells with P showed that the polypeptide carried a heat- and acid-stable phosphorylation and that during sucrose starvation the HPr became dephosphorylated. Antiserum raised to the HPr reacted on Western blots with HPrs from all oral streptococci tested, together with strains of and , but not with HPrs from or , nor with proteins from and various lactobacilli. The 5. HPr had a high content of alanine (17·2%) and was similar in overall amino acid composition to the HPrs from S. and The N-terminal residues (to 37) of the HPr showed strong sequence identity (82%) with the N-terminal sequence of HPr. It is suggested that HPr in is associated closely with the cytoplasmic membrane. Non-disruptive methods of removing cell-surface proteins from streptococci effect release of HPr and possibly other cytoplasmic components.


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