Fig. 2.

The 5′ Nun cross-linking. (A) Cross-linking strategy. Scheme I: Photoreactive TEC9 was first elongated by a radioactive substrate followed by Nun addition and UV irradiation. Scheme II: Nun was added to TEC9 assembled with RNA bearing a 5′ photoreactive group, followed by UV irradiation and incubation with radioactive substrate. (B) Phosphoimage of the reaction mixtures treated as in A after SDS denaturing and PAGE separation. Positions of RNAP cross-linked subunits and Nun are indicated along with protein size markers. (C) Nun cross-linking in TEC10, -11, and -12 following scheme I (A). (D) Partial hydroxylamine cleavage of the purified Nun cross-linked product. Arrow indicated the position of the cleavage site in Nun sequence.