Gtf enzyme activity assay. Overnight culture supernatant of strains in question, containing 3 μg total protein were used to precipitate Gtfs. To it, amylase and/or rAbpA was added to a final concentration of 50 μg/ml each. After 2 h at room temperature, precipitates were collected by centrifugation and resuspended in sample buffer and Gtf activity evaluated on SDS-polyacrylamide gel. Panel A. Lanes: 1, 2, and 3, supernatant from abpA- strain (ST); lanes 4,5, and 6, supernatant from Gtf-deficient strain. Panel B. Lanes 1, 2, and 3, supernatant from S. mutans. Panel C. SDS-PAGE gel of precipitates from supernatants stained with SYPRO red. Lanes 1, 2, and 3, supernatants from AbpA-deficient strains; lanes 4, 5, and 6, supernatants from gtf-negative strains of S. gordonii; lanes 7, 8, and 9, supernatants from S. mutans.