Definition of "mRNA"

When a cell “expresses” a gene, it translates the DNA first into a signature messenger RNA (mRNA) sequence and subsequently into a chain of amino acids that forms a protein.

2015 November 28, Ferris Jabr, “How Humans Ended Up With Freakishly Huge Brains”, in Wired‎

Because of their fragility, the mRNA molecules will quickly fall apart at room temperature. Moderna’s vaccine will need to be refrigerated, and should be stable for up to six months when shipped and stored at –4°F (–20°C).

2020 December 5, Jonathan Corum, Carl Zimmer, “How Moderna’s Vaccine Works”, in The New York Times‎