Antitermination

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Antitermination is the Prokaryotic cell's aid to fix premature termination of RNA synthesis during the transcription of DNA. It occurs when the RNA polymerase ignores the termination signal, and it provides a mechanism whereby one or more genes at the end of an operon can be switched either on or off, depending on the polymerase either recognizing or not recognizing the termination signal.

If the transcription is terminated prematurely (often after 100 - 1000 base pairs), the antiterminator binds to the transcribed RNA or upstream of the DNA terminator and "re-starts" the transcription.

Important in lambda-phage transcriptional regulation and also a form of positive regulation. In lambda-phage proteins N and Q are antiterminators. N protein prevents termination in early operons of lambda, but not in other phage or bacterial operons. Host RNA polymerase transcribes lambda genes and terminates at T sites.

Mechanism by which PN causes the RNA polymerase to ignore the terminator is not fully understood. In conjunction with other factors, it has an “antipausing” effect, which means that the probability of rho factor catching up with RNA polymerase is reduced. There might also a direct effect of PN on rho factor.