Precursor mRNA

As a precursor mRNA (English precursor messenger ribonucleic acid from the Latin praecursor, " precursor " ), short pre-mRNA, and pre-mRNA, generally synonymous with hnRNA (english heterogeneous nuclear ribonucleic acid ), the precursor form of eukaryotic mRNA is called.

The pre-mRNA is the first form of RNA, which is produced as a direct result of transcription in the context of gene expression of the genetic information (DNA) into proteins in eukaryotes, but not in prokaryotes (bacteria and archaea ). After complete processing of the " primary transcript " this messenger ribonucleic acid is then referred to as " mature mRNA " or simply mRNA. This is then available as part of the protein (protein synthesis) for the translation available.

HnRNA which is at the first translation step of transcription, as an intermediate product before, not all DNA segments which are located in a gene coding for proteins actually, only the portions referred to as exons. In transcription, the enzyme RNA polymerase II now copies the entire region of DNA, including all introns, so non- protein-coding sections. The product is referred to as hnRNA. Only by splicing, in which the introns excised, resulting RNA sequence is referred to as (mature ) mRNA.

Eukaryotes compared to prokaryotes

In eukaryotes, the pre-mRNA is by attaching a cap structure ( on the 5 ' end ), a poly ( A) tail and modified by splicing of the introns in the nucleus. This is partly already during transcription. The fully processed RNA is called mature mRNA. It is transported into the cytoplasm where translation begins.

In prokaryotes, no processing takes place, since the free DNA present in the prokaryotic cytoplasm, has in most cases had no introns, and thus mRNA is present directly after the transcription, which is usually still translated during transcription. This also makes it possible Genkontrollmechanismen such as the trp operon.