Question

CI has more binding capacity to the DNA than CRO- Justify the statement.

Answer 1

Using temperate Stapylococcus aureus phage,it is demonstrated that CI protein possesses two domains.It is composed of alpha-helix and beta-sheet at room temperature that uunfolds at temperatures above 39°C .CI binds to two sites in the phi11 CI-CRO intergenic region with variable affinity. These sites are O1 and O2 of the three homologous 15bp operators.The interactionof CI with these 2 sites binds to operater DNA as homodimer.

On the other hand,CRO posses a single domain structure-alpha helical structure that is moderately thermostable.Of the 3 homologous 15bp operators,CRO is only able to bind to O3 efficiently. This proves its less capacity of binding to DNA when compared to CI which binds to two operators.