What is the definition of heteronuclear RNA (hnRNA)?

Heteronuclear RNA (hnRNA) refers to the primary transcript produced from a gene before it undergoes any processing, which includes splicing and the removal of introns. This type of RNA contains both exons (the coding regions) and introns (the non-coding regions) immediately after transcription.

The defining characteristic of hnRNA is that it includes unspliced transcripts, which means that it has not yet been modified to remove the introns. This modification is essential for the RNA to become mature mRNA, which is subsequently translated into proteins. Only after the introns are removed and the exons are spliced together does the RNA become a mature form that is ready for translation.

Thus, the correct characterization of hnRNA as the newly transcribed mRNA that still retains introns makes it distinct from other forms of RNA that are fully processed and ready for translation.