Unformatted text preview: enough repressor to bind to the early operators
and prevent further early RNA synthesis
• The promoter used for establishment of lysogeny is
PRE, which lies to the right of PR and cro.
Transcription from this promoter goes leftward
through the cI gene. The products of the delayed
early genes CII and CIII also participate in this
process: CII, by directly stimulating polymerase to
binding to PRE and PI; CIII, by slowing degradation of
CII. Summary 3
• The promoter that is used to maintain lysogeny is
PRM. It comes into play after transcription from PRE
makes possible the burst of repressor synthesis that
establishes lysogeny. This repressor binds to OR1
and OR2 cooperatively, but leaves OR3 open.
• RNAP binds to PRM, which overlaps OR3 in such a
way that it contacts the repressor bound to OR2. This
protein-protein interaction is required for this
promoter to work efficiently.
• High levels of repressor can repress transcription
from PRM via DNA looping when repressor dimers are
bound to OR1, OR2, and OR3 Summary 4
• Whether a given cell is lytically or lysogenically infected by
phage λ depends on the outcome of a race between the
products of the cI and cro genes.
• The cI gene codes...
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- Spring '11