The S. mutans GBP-A is hypothesized to be constitutively expressed and
to contribute to the sucrose-dependent colonization of S. mutans. To
investigate GBP-A expression, a reporter gene encoding chloramphenicol
acetyltransferase (CAT) was placed downstream of the gbpA promoter an
d CAT activity was measured under conditions that would be associated
with the sucrose-dependent colonization of S. mutans. Expression of GB
P-A was optimal under anaerobiosis and neutral pH conditions, and corr
elated with optimal growth. The addition of sucrose to the growth medi
um did not elevate the expression of GBP-A.