Fig. 4. Variants that suppress the growth defect associated with the lack of PilQ and PilT show alterations in the expression, degradation and structure of the pilin subunit. (A) Immunoblot analysis of pilin subunits expressed by variants derived from the pilQ/pilT mutant (strain MW11, pilQ::mTncm21, pilTind) that no longer show a growth defect. Pilin-specific mAb MC02 was used to probe whole-cell lysates. Lane 1, wild-type (N400, recA6); lane 2, pilQ/pilT (MW11, pilQ::mTncm21, pilTind); lanes 3–14, variants isolated from MW11 (strains MW12–MW23, respectively). (B) Variants that suppress the pilQ/pilT-associated growth defect show multiple changes in the primary structure of pilin. The predicted amino acid sequence of pilin, expressed from pilE (designated pilEwt) of the parental pilQ/pilT strain is shown. Changes in the predicted primary structure of variant pilins, based on DNA sequence, are indicated. Periods (⋅) denote identical residues and dashes (–) represent gaps in the sequence. N-terminal sequences are not shown, as no changes were detected. No sequence is presented for MW19 as pilE was deleted in this strain.