FIG. 6.

Processing and secretion of nopaline VirB1(Q/S). (A) Amino acid sequences surrounding the VirB1* processing site for nopaline (Nop) and octopine (Oct) VirB1. The pair of alanines that constitute the VirB1* processing site in nopaline VirB1 are underlined. A single amino acid (*) in this region differs between nopaline and octopine. Numbers indicate the amino acid position. (B) Western blot of cell pellets probed with anti-nopaline VirB1 antibody. (C) Western blot of precipitated supernatant showing secreted VirB1*. For panels B and C: C58 -AS (lane 1), C58 +AS (lane 2), CB1001 (VirB1[Q/S]) +AS (lane 3), A348ΔB1 (VirB1[Q/S] +AS (lane 4). It is interesting that VirB1 (Q to S) without the signal peptide migrates slower than the wild-type nopaline VirB1 (without its signal peptide). However, once VirB1* is processed and cleaved from this precursor, both VirB1* derivatives that contain either Q or S very close to their N termini now migrate identically. Possibly, the Q-to-S mutation affects protein conformation, causing it to run anomalously. There also appears to be a difference between the nopaline and octopine strains in the migration of VirB1 (Q to S). Numbers to the right of each panel indicate molecular mass standards in kilodaltons. Arrowheads indicate VirB1*. AS is an inducer of vir expression. -, Culture not induced by AS; +, culture induced by AS.