Chapter 15, Problem 14P

Maltose utilization in E. coli requires the proteins encoded by genes in three different operons. One operon includes the genes malE, malF, and malG; the second includes malK and lamB; and the genes in the third operon are malP and malQ. The MalT protein is a positive regulator that controls the expression of all three operons; expression of the malT gene itself is catabolite sensitive.

a. What phenotype would you expect to result from a loss-of-function mutation in the malT gene?

b. Do you expect the three maltose operons to contain binding sites for CRP (cAMP receptor protein)? Why or why not? In order to infect E. coli, bacteriophage λ binds to the maltose transport protein LamB (also known as the λ receptor protein) that is found in the outer membrane of the bacterial cell. The synthesis of LamB is induced by maltose in the medium via expression of the MalT protein, as described above.

c. List the culture conditions under which wild-type E. coli cells would be sensitive to infection by bacteriophage λ.

d. E. coli cells that are resistant to infection by bacteriophage λ have been isolated. List the types of mutations in the maltose regulon (the set of all genes regulated by maltose) that λ-resistant mutants could contain.