Before revision:  Direct pairing was considered among other possibilities, but it seems hardly compatible with the DNA structure . Using quantum chemistry, molecular mechanics, and hints from recent genetics experiments (Nat.Commun.
After revision:  Direct pairing was considered among other possibilities, but it seems hardly compatible with the B-DNA structure because the sequence information is hidden when it is used for joining the two strands. Nevertheless, it has to be invoked to account for various biological data. Using quantum chemistry, molecular mechanics, and hints from recent genetics experiments (Nat.Commun.