Photochemical cross-linking of secondary structure in HeLa cell heterogeneous nuclear RNA in situ 1

The psoralen derivative 4'-hydroxymethyl-4, 5', 8-trimethylpsoralen (hydroxymethyltrioxsalen) has been used in experiments with isolated HeLa cell nuclei to photochemically cross-link double helical regions in heterogeneous nuclear RNA in situ. Although there are other self-complementary sequences in hnRNA that can form base-paired structures upon phenol deproteinization of annealing, the present in situ cross-linking results demonstrate that some double-stranded regions are an authentic component of native hnRNA structure. Moreover, these special regions of secondary structure are apparently highly accessible to chemical probes within the intact cell nucleus, despite the fact that hnRNA possesses a ribonucleoprotein organization.