title: The Xenopus 9 bp ribosomal terminator (T3 box) is a pause signal for the RNA polymerase I elongation complex.
abstract: In Xenopus, termination by RNA polymerase I (pol I) is mediated by the 9 bp sequence GACTTGCNC and RNA 3'-ends are formed -15-20 nt upstream of this terminator element. Here I show that this 9 bp element, also called the 'T3 box', is a pause signal for the elongating transcription complex. The two major transcripts in the paused complex have 3'-ends mapping to 15 and 21 nt upstream of the T3 box, remain bound to the template in 0.25% Sarkosyl, are subject to pyrophosphorolysis and can be chased into longer transcripts. Mutations that reduce overall termination also affect pausing, indicating that pausing is a limiting step in the termination process. Oligonucleotide competition experiments, furthermore, suggest that pausing requires a DNA binding factor. The data support a model in which the first step leading to transcription termination by pol I in Xenopus is pausing of the elongation complex upstream of the T3 box.
authors.affiliation: Scripps Research Institute, Department of Molecular and Experimental Medicine, La Jolla, CA 92037, USA.
authors.forename: P
authors.initials: P
authors.lastname: Labhart
mesh_terms: D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011401:Promoter Regions, Genetic; D012313:RNA / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D012318:RNA Polymerase I / Q000378:metabolism*; D012091:Repetitive Sequences, Nucleic Acid; D013698:Templates, Genetic; D014158:Transcription, Genetic; D014981:Xenopus / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; D012313:RNA; D004247:DNA; D012318:RNA Polymerase I