mRNAs

Messenger RNA (mRNA) is a single-stranded ribonucleic acid that conveys genetic information from DNA to the ribosome, where it guides protein synthesis. In cells, mRNAs encode the amino acid sequence of a protein and reflect the gene's transcriptional activity. Eukaryotic mRNAs are typically monocistronic and undergo extensive processing, whereas many prokaryotic mRNAs are polycistronic and can be translated while still being transcribed.

Most mature eukaryotic mRNAs contain a 5' cap, a 5' untranslated region (UTR), a coding sequence, a 3' UTR, and a poly(A) tail. The coding sequence begins with a start codon (usually AUG) and ends with a stop codon. The 5' cap and poly(A) tail cooperate with initiation factors to promote ribosome recruitment and mRNA stability.

In the nucleus, RNA polymerase II transcribes mRNA from DNA, then transcripts undergo capping, splicing to remove introns, and 3' polyadenylation. Splicing generates the mature mRNA; alternative splicing can yield different protein isoforms from a single gene.

Exported to the cytoplasm, the mRNA associates with ribosomes for translation. Initiation typically begins at the 5' cap, with ribosome scanning for a start codon. The elongating ribosome decodes codons into a polypeptide, which folds into its functional form after synthesis.

mRNA levels are controlled by transcriptional regulation and post-transcriptional processes. Elements in the 5' and 3' UTRs influence stability, localization, and translation efficiency. Degradation occurs via deadenylation, decapping, and exonucleolysis, yielding turnover rates that shape protein abundance.

mRNAs are central to gene expression and are exploited in research and medicine, including mRNA vaccines and therapeutic mRNAs that encode therapeutic proteins. Advances in mRNA biology continue to illuminate transcriptional regulation and translational control.