Distribution of coding sequences within the nuclear HnRNA—protein complexes

Most, if not all, of HnRNA is associated with a specific class of nuclear proteins [l-6]. The organiza- tion of the HnRNA within the RNP complexes is still unresolved. Depending on the nuclease activity of the respective tissues, the RNP complexes can be obtained in size classes > 250-30 S. The 30 S structures result from the degradation of that part of the HnRNA of the polymeric complexes which is easily accessible to the nuclear degradation enzymes [ 1,7]. The part of the HnRNA associated with the 30 S particles, very probably by virtue of its tight association with the protein moiety, is resistant to the action of the nucleases. As the HnRNA is composed both of cod- ing sequences as well as of nucleotide stretches of unknown function, we were interested in obtaining data on whether there was a preferential en~chment of specific sequences in the 30 S RNP particles. To this end, we have compared the hybridization of cDNA synthesized from polysomal poly(A)’ RNA to RNA isolated from 30 S and 80-l 50 S RNP particles. The results suggest that a higher propor- tion of coding RNA sequences is present within the 30 S RNP structures than in the regions of the HnRNA exposed to nuclear degrading enzymes. 2. Materials