A possible regulatory mechanism in RNA processing and its implication for posttranscriptional sequence control during differentiation of cell function.

1. This paper is concerned with the possible molecular mechanism for RNA processing including posttranscriptional sequence control underlying the differentiation of cell functions. 2. It was previously postulated that intramolecular double-stranded hairpin structures present at 5'- and 3'-terminal regions of a 'pre-mRNA' are key elements for RNA splicing [24]. 3. In this paper the possibility is considered that the splicing of 'pre-mRNA' can be regulated in such a way that the formation of the proper double-stranded hairpin structures is prevented by the binding of low-molecular-weight nuclear RNA (LnRNA) to the terminal regions and/or to the nucleotide sequences around the exon-intron and intron-exon joint sites of the 'pre-mRNA' molecules. 4. Complementarity assessment of nucleotide sequences of rat preproinsulin 'pre-mRNA' and rat LnRNA, i.e. Ul, showed that Ul RNA is capable of forming stable double-standard intermolecular structures around the joint sites of preproinsulin 'pre-mRNA' and may prevent the formation of intramolecular double-stranded structures required for RNA splicing. This may imply a regulatory (inhibitory) role for Ul RNA in the processing of 'pre-mRNA'. 5. A possible regulatory role of LnRNA in RNA splicing is discussed in relation to the determination of the mRNA population to be translated in the cytoplasm during differentiation of cell functions.