Figure 1.

Commonly used terms in the study of mRNA biogenesis and regulation. An mRNA begins its life with transcription and initially exists as a premature mRNA (pre-mRNA). The pre-mRNA includes more sequence than the mature mRNA will contain. The pre-mRNA is processed, spliced, and edited to give rise to the mature mRNA. Several commonly described features of the mature mRNA are indicated, including the trimethylguanosine “cap,” spliced leader (blue, which is appended after excision of the outron), 5′ UTR (the portion of the mRNA upstream of the start codon), CDS (green, coding DNA sequencing also called open reading frame (ORF), 3′ UTR (yellow, the region of mRNA downstream of the stop codon) and untemplated poly(A) tail. For simplicity, the pre-mRNA and mRNA are shown as discrete entities, though there is evidence that mRNA maturation occurs cotranscriptionally. The mature mRNA is exported from the nucleus, possibly translated, and eventually degraded.