Template activity of synthetic deoxyribonucleotide polymers in the eukaryotic DNA-dependent RNA polymerase reaction

Template specificities of the eukaryotic DNA-dependent RNA polymerases A and B from rat liver, pea, and cauliflower have been investigated using synthetic polydeoxyribonucleotides. Polymerases A and B from the three species exhibit different specificities for single-stranded homopolymers: polymerase A preferentially reads poly(dT) and poly (dC). and polymerase B poly (dC). This preferential reading appears to be a property of eukaryotic DNA-dependent RNA polymerases. Polymerases A and B transcribe synthetic polyribonucleotides also, but at a reduced rate. The polyribonucleotides which can be read by DNA-dependent RNA polymerases have a base sequence similar to that of the polydeoxyribonucleotides, which are effeciently transcribed, suggesting that the base sequence of the template rather than its conformation is crucial in the template specificity for synthetic polymers. Competition experiments with polydeoxyribonucleotides indicate that the enzymes have different binding specificities, which are not the same as their template specificities.