A. Wild-type Zif268 binds the sequence 5’-GCGTGGGCG-3’. Rebar is using phage display to generate an altered version of Zif268 that binds the sequence 5’-GCGTGGGAC-3’. He creates a library in which residues Arg 18, Asp 20, Glu 21, and Arg 24 are randomized. Why did he choose these residues? b. if you were generating a Zif268 protein that binds the sequence 5’-GCGGACGCG-3’, what residues would you randomize? Justify your answer.
c. The selected phage from part a have the following sequences:

Position: 18 20 21 24
S Q N R
D A N R
D R N R
D S N R
S S N R
S T N R
T A N R
T P N R
What do the consensus sequences at positions 21 and 24 indicate?
d. Suppose Rebar had created a library in which His 25 and His 29 were randomized. What sequences might you expect to be selected from this library? Why?