Identification of <i>std</i> operon products involved in SPI-1 repression.

<p>A. ß-galactosidase activities of <i>invF::lac</i> and <i>sipB::lac</i> fusions in a strain containing an intact <i>std</i> operon (control) and in a isogenic strain lacking the entire <i>std</i> operon (Δ<i>std</i>). Black and white histograms represent ß-galactosidase activities in Dam⁺ and Dam⁻ backgrounds, respectively. Asterisks above columns indicate that the differences observed are statistically significant (P<0.005). B. Regulation of an <i>invF::lac</i> fusion by Dam methylation in strains carrying in-frame deletions in individual <i>std</i> genes. Histograms represent ß-galactosidase activities in a Dam⁺ background (black) and in a Dam⁻ background (white). Asterisks above columns indicate that the differences observed are statistically significant (P<0.005).