Answer:
c. Major groove
Explanation:
The interaction surfaces of proteins are, in general, varied. From the point of view of the secondary structure, the surfaces of the proteins are formed by the surfaces of their α helices, β sheets and loops that conform them. The surfaces of the DNA molecules are less varied: the B-DNA helix has a monotonous “screw” shaped surface with phosphoribose ridges between which two grooves (major and minor) are formed. The difference between different nucleotide sequences can only be seen from outside in the major groove, where the bases appear. The surfaces of RNA molecules that possess tertiary structure (such as t-RNA) are almost as complex as that of proteins.
Since the major groove is the only site where the bases are accessible from outside the B-DNA without distorting it, the major groove constitutes the main recognition site. As the interaction between molecules is stronger if their surfaces are complementary, the protein-DNA interaction usually occurs by filling the major groove.
