1. The following genetic elements are important for the lambda growth. Describe the role each plays and indicate the consequences of a loss of function mutation on (i) the lysis/lysogeny decision upon infection and (ii) induction by UV light. Also indicate whether the element acts in cis or trans.

    1. sib

    2. N 

    3. PRM

    4. Nut 

    5. bacterial recA 

    6. PI 

       

  2. Four different types of clear mutations are found in lambda (the clear phenotype indicates that no lambda lysogens form): three of these (lambda_cI, lambda_cII , and lambda_cIII) are defective in the cI, cII, and cIII genes, respectively; the fourth (lambda_cy) is defective in PRE so that it no longer binds the cII product.

    1. Which mutations act in cis?  Which mutations act in trans?

    2. Which of these, if any, would allow a mutant phage to bypass λ immunity and grow on a lambda lysogen?  Explain.

    3. The following double infections were tested to look for complementing gene action. For each indicate whether a lysogen would form and why.

      1. lambda_cI and lambda_cII 

      2. Lambda_cy and lambda_cI 

      3. lambda_cy and lambda_cII

       

  3. Compare and contrast the cro and cI genes

     

  4. Answer TRUE or FALSE.  If the statement is TRUE, explain or give a supporting example.  If the statement is FALSE, either correct the statement or give a counterexample.

    1. Mutation of the phage λ cII gene would lead to lysogeny.

    2. Mutations eliminating the cro gene would act in a trans dominant fashion to the wild-type gene.

    3. Mutation of the phage λ cIII gene would lead to lysogeny.

     

  5. Several genetic components in λ can be mutated to give constitutive lytic growth. For each of the following explain how the mutation(s)  would cause constitutive lytic growth and why it would be expressed in the fashion it is.

    1. A recessive mutation

    2. A recessive mutation in a different genetic component

    3. A cis dominant mutation

    4. A cis dominant mutation in a different genetic component

    5. A trans dominant mutation

       

Answers