Page "Messenger RNA" Paragraph 4

Transcription is when RNA is made from DNA.

During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed.

This process is similar in eukaryotes and prokaryotes.

One notable difference, however, is that prokaryotic RNA polymerase associates with mRNA-processing enzymes during transcription so that processing can proceed quickly after the start of transcription.

The short-lived, unprocessed or partially processed product is termed precursor mRNA, or pre-mRNA ; once completely processed, it is termed mature mRNA.