The recognition sites for the restriction enzymes BamHI, XbaI and BglII are G^GATCC, T^CTAGA and A^GATCT, respectively. Which enzymes leave compatible ends that can be ligated together? (A) All of these enzymes leave ends that are compatible with ends generated by the others. (B) None of the enzymes produce compatible ends. (C) Only BamHI and BglII fragments are compatible. (D) Only BamHI and XbaI fragments are compatible. (E) Only BglII and XbaI fragments are compatible.

(C) Only BamHI and BglII fragments are compatible.

Explanation:

First we can visualize how the enzymes cut by completing the strand below and cutting where indicated. The three enzymes cut with cohesive ends.

Then we can complete the sense of the strands and serach compatible ends. Keep in mind that we can only join 5 'ends with 3' ends.

BamHI = G ... 3' 5' ... GATCC

CCTAG ... 5' 3' ... G

XbaI = T ... 3' 5' ... CTAGA

AGATC ... 5' 3' ... T

BglII = A ... 3' 5' ... GATCT

TCTAG ... 5' 3' ... A

In bold, leave the bases that remain in single strand and must be compatible with those of the other end.

To be compatible they must be complementary bases. A with T and C with G.

Now you can see that only BamHI fragments are compatible with those of BglII.