Effect of LDEVFL mutations on disulfide cross-linking between DrrA(S319C) and DrrB(S23C). Each LDEVFL mutation was introduced into a strain containing A(S319C)B(S23C) for disulfide cross-linking experiments. A, i, effect of L303V mutation on disulfide cross-linking. Lanes 1 and 2, A(Y89C)B(S23C); lanes 3–5, A(319C)B(S23C); lanes 6–8, A(S319C)B(S23C) containing the L303V mutation. Western blot analysis was carried out with anti-DrrA antibody. A, ii, histogram showing the efficiency of cross-linking in wild type and mutant. The wild type efficiency was designated as 1. The data presented are averages of three independent experiments. Error bars, S.D. B and D, effect of D304N and X310–312A (L310A/T311A/G312A) on disulfide cross-linking, respectively. Data are organized as in A. C and E, effect of X306–308A and ΔLDEVFL on disulfide cross-linking, respectively.