II recognizes the complex between the bound TATA transcription factor and the DNA binding site. Once RNA polymerase recognizes and attaches to the promoter region, it probably associates with other transcription factors before RNA synthesis begins. When active RNA polymerase binds to a promoter, the enzyme separates the two DNA strands at the initiation site, and transcription begins. During transcription, mRNA grows about 30 - 60 nucleotides per second. Following in series, several molecules of RNA polymerase II can simultaneously transcribe the same gene.
Cells can thus produce particular proteins in large amounts.
The growing RNA strands hang free from each polymerase.