Analysis of exponential-phase Mga-regulated gene expression in serotype M6 KSM148 sptR mutants. (A) GusA activity of whole-cell lysates from wild-type KSM148 (148), mga-inactivated KSM148.586 (586), and the 12 sptR mutants (1R, 2R, and 4R to 13R). Whole-cell lysates from exponential-phase cells were examined in a liquid GusA assay for the production of β-glucuronidase. (B) Northern analysis (1 μg of total RNA) of serotype M6 KSM148 sptR mutants for emm6 transcript levels (top). Northern blots were stripped and reprobed for 23S RNA as a control for loading. Mga protein levels (bottom) in each lysate were determined by Western blotting (7 μg of total protein), with an antibody to a peptide of Mga used as a probe. (C) Northern analysis (1 μg of total RNA) of serotype M1 SF370 sptR mutants for emm1 transcript levels (top). Northern blots were stripped and reprobed for 23S RNA as a control for loading (bottom).