Ribohomopolymer formation as a source of error in the radioactive precursor incorporation studies of nuclear DNA-dependent RNA synthesis

Isolated rat liver nuclei contain ribohomopolymer polymerases with relative activities in the following order: Poly (A) (100%) > Poly (C) (62%) > Poly (U) (34%) > Poly (G) (13%). Because these enzymes share the same substrates with the nuclear DNA-dependent RNA polymerases in nuclei, labelled precursor is therefore concurrently incorporated into both RNA and ribohomopolymer. Thus, experiments designed to study DNA-dependent RNA synthesis are subjected to error. It is estimated when [¹⁴C]ATP is used as the labelled precursor, the error is as high as 35%; [¹⁴C]CTP, 20%; [¹⁴C]UTP or [¹⁴C]GTP, 10%.