Why would phage ? need to synthesize more cI repressor during establishment of l
ID: 134842 • Letter: W
Question
Why would phage ? need to synthesize more cI repressor during establishment of lysogeny, early in infection, rather than in maintenance of the lysogenic state?
Why would phage need to synthesize more cI repressor during establishment of lysogeny, early in infection, rather than in maintenance of the lysogenic state?
The genes of phage multiplication are repressed by a cascade of different co-repressors, which are induced by the original cI repressor, so once they are activated, a lower level of cI will suffice. CI and cro genes compete to establish the phage lifestyle, so a large amount of cI repressor is needed to overcome cro activity, but afterward a lower level of cI will suffice. CI acts as a transcriptional activator of genes that promote lysogeny, so after they are activated and overcome phage multiplication genes a lower level of cI will suffice. The genes of phage multiplication are repressed by proteolytic cleavage, which is an irreversible process that is induced by the cI repressor, so once the majority has been degraded, a lower level of cI will suffice.Explanation / Answer
Option 3rd is the correct answer. CI act as atranscriptional activator and and in order to establish and maintain lysogent it binds to 6 operator sequence of viral genome.The production of CI protein regulated by the OR3 sequence. At low concentrations of CI protein, OR3 is unoccupied and CI protein is produced. The production of CI protein ceases when the concentrations are sufficient to occupy OR3.
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