Figure 7.

Possible orientations of H-DNA relative to direction of transcription. RNA polymerase (shown as gray triangle on the template strand pointing in the direction of elongation) can either proceed from a donor part of the H-palindrome toward its acceptor part (d→a), or from an acceptor half to the donor (a→d) using either homopyrimidine (y), or homopurine (r) strands as templates. This results in four possible combinations of transcription substrates. Only substrates from the first column were studied in the current work.