Messenger RNA
Messenger RNA, or mRNA, is the RNA copy of genetic information that ribosomes read to build proteins.
What messenger RNA is
Messenger RNA is a single-stranded RNA molecule that carries protein-coding information. It is made from a DNA template during transcription and read by ribosomes during translation. In that sense, mRNA is a working copy of genetic instructions rather than the long-term archive itself.
From DNA to mRNA
During transcription, RNA polymerase copies one strand of DNA into a complementary RNA transcript. The RNA sequence reflects the information in a gene, but uses uracil instead of thymine. In bacteria, this transcript may be translated almost immediately; in eukaryotes, it usually undergoes processing before it is exported from the nucleus.
Eukaryotic processing
A typical eukaryotic protein-coding mRNA is shaped by several processing steps. A 5' cap is added, introns are removed by splicing, and a poly(A) tail is added at the 3' end. These features help stabilize the mRNA, support export from the nucleus, and influence how translation begins.
Coding region and UTRs
Mature mRNA usually includes untranslated regions, or UTRs, on both sides of the coding sequence. The coding region begins at a start codon and ends at a stop codon. The UTRs do not encode the protein sequence directly, but they can strongly affect mRNA stability, localization, and translation efficiency.
Reading codons
During translation, the ribosome reads mRNA in codons, groups of three nucleotides. Transfer RNAs match anticodons to those codons and deliver amino acids. The order of codons in the mRNA therefore helps determine the order of amino acids in the protein.
Monocistronic and polycistronic mRNA
Many eukaryotic mRNAs are monocistronic, meaning one mRNA usually encodes one main protein. Many bacterial and archaeal transcripts are polycistronic, meaning one mRNA can contain multiple coding regions, often from genes organized in an operon. This difference affects how gene expression is coordinated.
mRNA lifetime
mRNA molecules are temporary. Some are degraded quickly, while others persist long enough to be translated many times. Cells regulate mRNA lifetime through sequence elements, RNA-binding proteins, small RNAs, and decay pathways, making mRNA abundance a major layer of gene expression control.
Why it matters
Messenger RNA connects stored genetic information to active protein production. It is central to transcription, translation, RNA sequencing, gene regulation, and modern biotechnology. Understanding mRNA helps explain how cells change behavior without changing the DNA sequence itself.