Do Hoogsteen base pairs occur in DNA?

The importance of the Watson-Crick complementary base-pairing scheme has rather overshadowed alternative types of base pairs in DNA. One of these alternative base pairings, which is known as Hoogsteen pairing, is now receiving attention. Its presence in crystals of oligonucleotides bound to some antibiotics, and its possible existence in solution (and within long DNA fragments) remains to be unambiguously estimated. However, variability in DNA conformation appears to play an important biological role, and thus we should consider the presence of Hoogsteen base pairs as an interesting factor in inducing such changes.