Lectin binding of wild-type CB15, YB3558 and YB3559. Wild-type, YB3558 and YB3559 cells were treated with FITC-conjugated WGA lectin and imaged as described in the Methods. WGA lectin binds to holdfast and is seen as a fluorescent focus when imaged (example indicated with white arrow, WT panel). Wild-type cells display holdfast at the tips of stalks, while the YB3558 mutant produces no holdfast. Complementation of YB3558 with a ctrA gene under native control (YB3559) restores holdfast synthesis.