Heteroduplex analysis of the Xenopus RNA polymerase I terminator.

Recent results showed that the Xenopus ribosomal terminator, a conserved 9-bp element ("T2/T3 box"), is a pause signal for the RNA polymerase I-elongation complex (Labhart, P. [1995] Nucleic Acids Res. 23, 2252-2258). Since the terminator is known to function only in one orientation, it was of interest to investigate whether the 9-bp pause element had to be present in both DNA-strands to mediate termination of RNA polymerase I-transcription. The present heteroduplex analysis of the terminator shows that only the double-stranded 9-bp element constitutes a functional terminator. Any single-stranded mutation had the same down-effect as the corresponding double-stranded (homoduplex) mutation. Models for termination by Xenopus RNA polymerase I that are supported or eliminated by the present results are discussed.