premessenger

Premessenger is a term used in molecular biology to refer to the precursor form of messenger RNA, commonly known as pre-mRNA or the primary transcript. In eukaryotic cells, the initial RNA product of transcription by RNA polymerase II is often called heterogeneous nuclear RNA (hnRNA) and serves as the premessenger before processing.

Biogenesis and processing of premessenger RNA involve several steps. The primary transcript contains both exons, which encode protein information, and introns, which are non-coding sequences. The premessenger undergoes RNA processing in the nucleus, including 5' capping, 3' polyadenylation, and intron removal by the spliceosome. Alternative splicing can produce multiple mature mRNA variants from a single premessenger, expanding the diversity of the proteome. In some cases, RNA editing also modifies bases after transcription. The processed, mature mRNA is then exported to the cytoplasm for translation.

Function and context: The premessenger RNA stage is a key regulatory checkpoint in gene expression, allowing cells to control which protein products are produced. In contrast, in most prokaryotes there is no extensive pre-mRNA processing, as transcription and translation are more tightly coupled and intron processing is less common.

Terminology: While “premessenger RNA” is used to describe the precursor form, most contemporary genetics literature prefers pre-mRNA or hnRNA to denote the same concept. See also pre-mRNA, mRNA, RNA processing, and alternative splicing.