Abstract
We have previously shown that plant RNA polymerase II preferentially forms ternary transcription complexes on a cloned fragment of the cauliflower mosaic virus genome in the presence of a particular dinucleotide/purine NTP combination (ApG + ATP). This preferential interaction is observed when the viral sequences are present on a discrete circular molecule. Deletion of a 205-bases-pair region abolishes this selectivity. The deleted region contains a considerable number of symmetrical or repeating elements. The use of nuclease S1 as a probe shows that this region contains a homopurine-homopyrimidine sequence which is extremely sensitive to this enzyme, indicating its capacity to adopt a non-B DNA conformation. A possible alternative structure of these sequences, which may explain the preferential intereaction with the RNA polymerase, is presented.