Replication and transcription of polynucleotides containing ethenocytosine, ethenoadenine and their hydrated intermediates.

Replication with Escherichia coli DNA polymerase I (Pol I) and transcription with DNA-dependent RNA polymerase from Escherichia coli or calf thymus, using as templates synthesized ribo- or deoxyribopolynucleotides containing 1,N6-ethenoadenine (epsilon A) or 3,N4-ethenocytosine (epsilon C), showed that only epsilon C could direct significant misincorporation. The hydrated intermediate of epsilon C caused errors only upon transcription, but not upon replication. epsilon A was a very poor mutagen as assessed by replication with Pol I. Transcription of polynucleotides containing epsilon A under error-prone conditions caused frequent A misincorporation which could not be detected in replication assays. It is concluded that epsilon C may lead to point mutations, specifically directing the misincorporation of thymine. The analogous derivative, epsilon A, is bulky and is likely to be bypassed rather than read. This mechanism could cause frameshift mutation, as generally found for other bulky adducts.