Synthesis of amplified DNA that codes for ribosomal RNA.

During the amplification stage in ovaries, the complete repetitive unit of the DNA that codes for ribosomal RNA in Xenopus appears to be transcribed. This large RNA transcript is found in a complex with DNA. Substitution experiments with 5-bromodeoxyuridine do not show any evidence that a complete amplified cistron is used as a template for further amplification. A derivative of rifampicin, 2',5'-dimethyl-N(4')benzyl-N(4')[desmethyl] rifampicin, preferentially inhibits the DNA synthesis responsible for ribosomal gene amplification. These results are consistent with the hypothesis that RNA-dependent DNA synthesis is involved in gene amplification.