Editing Primary transcript (section)

{{Short description|RNA produced by transcription}}
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[[File:Pre-mRNA.svg|thumb|Pre-mRNA is the first form of RNA created through transcription in protein synthesis.  The pre-mRNA lacks structures that the messenger RNA (mRNA) requires. First all introns have to be removed from the transcribed RNA through a process known as splicing. Before the RNA is ready for export, a Poly(A)tail is added to the 3' end of the RNA and a 5' cap is added to the 5' end.]]
[[File:Transcription label en.jpg|thumb|Micrograph of gene transcription of ribosomal RNA illustrating the growing primary transcripts]]

A '''primary transcript''' is the single-stranded ribonucleic acid ([[RNA]]) product synthesized by [[Transcription (genetics)|transcription]] of [[DNA]], and processed to yield various mature RNA products such as [[mRNA]]s, [[tRNA]]s, and [[rRNA]]s. The primary transcripts designated to be mRNAs are modified in preparation for [[Translation (biology)|translation]]. For example, a precursor mRNA (pre-mRNA) is a type of primary transcript that becomes a messenger RNA (mRNA) after [[Post-transcriptional modification|processing]].

Pre-mRNA is synthesized from a [[DNA]] template in the [[cell nucleus]] by [[transcription (genetics)|transcription]]. Pre-mRNA comprises the bulk of heterogeneous nuclear RNA (hnRNA). Once pre-mRNA has been completely [[Post-transcriptional modification|processed]], it is termed "[[mature messenger RNA]]", or simply "[[messenger RNA]]". The term hnRNA is often used as a synonym for pre-mRNA, although, in the strict sense, hnRNA may include nuclear RNA transcripts that do not end up as cytoplasmic mRNA.

There are several steps contributing to the production of primary transcripts. All these steps involve a series of interactions to initiate and complete the transcription of [[DNA]] in the [[Cell nucleus|nucleus]] of [[eukaryotes]]. Certain factors play key roles in the activation and inhibition of transcription, where they regulate primary transcript production. Transcription produces primary transcripts that are further modified by several processes. These processes include the [[five-prime cap|5' cap]], [[Polyadenylation|3'-polyadenylation]], and [[alternative splicing]]. In particular, alternative splicing directly contributes to the diversity of mRNA found in cells. The modifications of primary transcripts have been further studied in research seeking greater knowledge of the role and significance of these transcripts. Experimental studies based on molecular changes to primary transcripts and the processes before and after transcription have led to greater understanding of diseases involving primary transcripts.