Dependence of 4'-(hydroxymethyl)-4,5',8-trimethylpsoralen photoaddition on the conformation of RNA

Abstract
The photoaddition of 4''-(hydroxymethyl)-4,5'',8-trimethylpsoralen (HMT) to different conformational states of RNA was studied. Poly(U), poly(A,U) (random copolymer), poly(A-U) (alternating copolymer), poly(A).cntdot.poly(U) (double stranded), and poly(U).cntdot.poly(A).cntdot.poly(U) (triple stranded) were reacted with HMT at different temperatures and salt concentrations. The conformation of the polymers was monitored by UV absorption and circular dichroism. The rate of HMT photoaddition changed dramatically at structural transitions in the RNA. The alternating copolymer poly(A-U) had the highest rate of addition. Low salt and temperature produced maximal incorporation.