(a) Base sequences of the DNA template strand and of the RNA transcript in tR2 transcription termination site from bacteriophage λ. The GC-rich sequence with inverted symmetry is boxed. The sequences corresponding to the A-rich tract are shown in bold. Transcription terminates at one of the two positions indicated by a “t”. The most frequent termination point is at the first of these positions.
(b) Base sequence and numbering of base pairs in the RNA-DNA hybrid investigated.
(c) The structures of GC and AU/T base pairs with the imino protons highlighted.