Characterization of ΔI-SM::CBD in front of different cysteines of I-TevI. (A) Ligation and cleavage products of pMBP-TevR27A::ΔI-SM::CBD. N-Ex, C-Ex and N-Ex/C-Ex are the N-extein, C-extein and ligated exteins of the I-TevI derivatives, respectively. N-I and C-I are the N- and C-terminal halves of the ΔI-SM intein, respectively. (B) SDS–PAGE of MBP-I-TevR27A::ΔI-SM::CBD at seven different cysteines of I-TevI after affinity chromatography on amylose resin, before in vitro splicing. M1, protein molecular weight standards, high range (Gibco BRL); M2, broad range protein markers (NEB). Lane 1, Cys39; lane 2, Cys58; lane 3, Cys100; lane 4, Cys153; lane 5, Cys164; lane 6, Cys207; lane 7, Cys214. Symbols for precursor and products are as designated in (A).