RNA transcripts of the dna that are in some unfinished stage of post-transcriptional processing (rna processing, post-transcriptional) required for function. rna precursors may undergo several steps of rna splicing during which the phosphodiester bonds at exon-intron boundaries are cleaved and the introns are excised. Consequently a new bond is formed between the ends of the exons. Resulting mature RNAs can then be used; for example, mature mRNA (rna, messenger) is used as a template for protein production.