27. In homologous genetic recombination, RecA protein is involved in:
(A) formation of Holliday intermediates and branch migration.
(B) introduction of negative supercoils into the recombination products.
(C) nicking the two duplex DNA molecules to initiate the reaction.
(D) pairing a DNA strand from one duplex DNA molecule with sequences in another duplex, regardless of complementarity.
(E) resolution of the Holliday intermediate.