P L P R and P RE promoters producing the Immediate Early IE transcripts the N aNtiterminator and cro Control of Repressors operator genes The N protein is an ID: 933303
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Slide1
Transcription starts from the constitutive
PL, PR and PRE promoters producing the ‘Immediate Early -IE' transcripts: the N (aNtiterminator) and, cro (Control of Repressor’s operator) genes. The N protein is an antiterminator, and functions to extend the reading frames passing 2 IE genes: N & cro. N binds to the two Nut (N utilisation) sites, one in the N gene in the PL reading frame, and one in the cro gene in the PR reading framecro binds to OR3 preventing access to the PRM promoter preventing expression of the cI gene.
Slide2The cII and cIII genes are needed to establish lysogeny
The delayed early gene products cII and cIII are necessary for RNA polymerase to initiate transcription at the promoter PRE. cII acts direct at the promoter and, cIII protects cII from degradation. Transcription from PRE leads to synthesis of repressor and also blocks the transcription of cro.
Slide3Lysogeny
is maintained solely by cI (clear1). cI represses transcription from PL and PR while upregulating and controlling its own expression from PRM.Cl is a transcription inhibitor, binds OR1, OR2 and OR3 (affinity OR1 > OR2 = OR3). At low concentrations blocks the pR promoter (preventing cro production).It is, therefore, the only protein expressed by lysogenic phage.
Slide4