Abstract
The gene spa P (formerly designated as spa P1) encoding the M r 185,000 surface antigen (I/II) of Streptococcus mutons, serotype c (NG5), has been sequenced. The gene (4683 bp) encodes a protein of 1561 amino acid residues including putative signal peptide (residues 1–38) and transmembrane (residues 1537–1556) sequences. The N-terminal region (60–550) has alanine-rich repeats and is predicted to be α-helical. However, the C-ternunal region (800–1540) is proline-rich and favours an extended structure. Except for a short central variable region the sequences appear to be highly conserved for S. mutans serotype c. N-Tenninal sequencing of separated antigen I and antigen II polypeptides suggests that the former represents the N-terminal and the latter the C-terminal portions of the intact antigen.
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