Specific regions of the intervening sequences of beta-globin RNA are resistant to nuclease in 50S heterogeneous nuclear RNA-protein complexes.

The specific assembly of heterogeneous nuclear RNA-protein complexes (hnRNPs) containing precursor beta-globin RNA was investigated by using the 50S hnRNP released from chicken reticulocyte nuclei by endogenous nuclease. The nuclease-resistant regions were mapped on adult beta-globin intervening sequences (IVS) at the resolution of nucleotides with an RNA mapping method [Patton, J. R. and Chae, C.-B. (1983) J. Biol. Chem. 258, 3991-3995]. We found that there is one 28-nucleotide-long nuclease-resistant region in the first IVS and there are four nuclease-resistant regions in the second IVS. Of particular interest is the presence in 50S hnRNP of a nuclease-resistant region (24-28 nucleotides long) in both IVS immediately upstream from the putative lariat branch site in an RNA splicing intermediate. Our results demonstrate that hnRNPs containing precursor beta-globin RNA are, like those containing mature beta-globin RNA, assembled in a site-specific manner.