Fig. 3.

Nun cross-linking with photoreactive probes introduced at 5′, 3′, and both 3′ and 5′ termini. (A) The scheme for Nun 3′ cross-linking as in TEC12. The structure of the photo–cross-linkable 3′ RNA residue is presented. The double 3′, 5′ cross-linking was performed similarly, but using an RNA 5′ photoreactive derivative (Fig. 2) in the above scheme. (B) Cross-linking results. Cross-linked radioactive products are indicated. “a,” “b,” and “c” represent minor radioactive products detected under various cross-linking conditions. (C) Effect of amino acid substitutions in Nun (K106/107A) and RNAP (β′R322H) on RNA–Nun cross-linking. The cross-linking reaction was performed at 20 °C in transcription buffer in the absence of Mg²⁺ with 2 µM Nun. Quantification of RNAP and Nun cross-links is presented at the bottom of the panel.