Transcription in Lambda Phage

Transcription in Lambda Phage

	Transcription in Lambda Phage - Lytic development has two phages the early period and the late period. The early period is the time before replication of phage DNA. The late period is the time from replication to maturation. Different genes are expressed during these two periods. There are three classes of genes, immediate early genes, delayed early genes and late genes. (i) The immediate early genes, N and cro, are, transcribed during the early period.
(ii) The delayed early genes lie to the left of N and the right of cro. The cIII, gam, bet, exo, del, xis and int genes are, on the left of the immunity operon. ell, O, P and Q are on the right of the immunity operon. (iii) The ate genes are transcribed during the late period. The three classes of genes transcribe three corresponding classes or mRNAs, immediate early delayed early and late messengers. Early messengers are transcribed from both left and right strands; while late messengers are transcribed only from the right strand. Transcription, of the right strand proceeds from left to right, while transcription ofthe left strand proceeds in the opposite direction.
In vitro expeiments show that two immediate early RNAs are formed In the presence of termination factor rho (P) (i) The leftward transcription starts from the, left promoter (PL) and continues through gene N to the left terminator (tL). The transcription produces 12S' RNA. (ii) The rightward transcription begins from the right promoter (PR) ansi extends through gene ero to the first right terminator (tRI).
The transcription produces a 7S RNA molecule. Some transcription may continue through genes O and P to the second right terminator (tR2). Transcription of the delayed early genes required the gene N product (gpN). This protein acts as an antiterminator and neutralizes the terminators tL, tRI and OO. It thus controls the expression of most viral functions. This appears to be brought about by the interaction of gpN with RNA polymerase at the promoters, forming a rho resistant complex.
	Prevention of termination permits transcription in both leftward and-, rightward directions leftward transcription extends into the b2 region and rightward transcription to gene Q. The Q gene product (gpQ) is a late antiterminator which neutralizes the third right terminator (tR3). This permits transcription to proceed through the vegetative component genes to gene J and into the b2 region.

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