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lähettiRNA, known in English as messenger RNA (mRNA), is a single-stranded RNA molecule that carries genetic information from DNA to the ribosome, where it serves as a template for protein synthesis. In Finnish biology usage, lähettiRNA is the term for mRNA.

In eukaryotes, lähettiRNA is transcribed by RNA polymerase II and undergoes processing before leaving the nucleus. It receives a 5' cap, a 3' poly(A) tail, and contains untranslated regions (5' UTR and 3' UTR) flanking an open reading frame that encodes a protein. Introns are removed by splicing to produce the mature mRNA. In prokaryotes, mRNA molecules are typically shorter, often lack introns, and can be polycistronic, encoding multiple proteins in one transcript.

The lifecycle of lähettiRNA begins with transcription in the nucleus (in eukaryotes) or directly in the cytoplasm (in many prokaryotes), followed by processing and export. It associates with ribosomes in the cytoplasm, where tRNAs deliver amino acids according to the encoded sequence, producing a polypeptide. The mature protein folds and often becomes functional, while the mRNA is eventually degraded by cellular nucleases, allowing dynamic control of protein production.

Regulation of lähettiRNA abundance and translation is influenced by sequence elements in the UTRs, the 5' cap and poly(A) tail, RNA-binding proteins, and microRNAs. Beyond its basic role in gene expression, mRNA is also used in biotechnology and medicine, notably in vaccines and therapeutic research, where synthetic mRNA codes for specific antigens or therapeutic proteins.