title: Xenopus tropicalis U6 snRNA genes transcribed by Pol III contain the upstream promoter elements used by Pol II dependent U snRNA genes.
abstract: We have cloned and sequenced a 977bp DNA fragment, pXTU6-2, that represents the transcription unit for a Xenopus tropicalis U6 RNA gene. This basic repeating unit is reiterated ca.500-fold per haploid genome. Oocyte injections of pXTU6-2 led to the transcription of a mature-sized U6 RNA that, however, lacked internal 2'-O-methylations. These posttranscriptional modifications of U6 RNA might be cytoplasmic and could require its association with U4 RNA to be accomplished. The low alpha- amanitin sensitivity of U6 RNA synthesis in oocytes suggested that U6 RNA is transcribed by RNA polymerase III, consistent with features of the U6 RNA molecule which also contains a Box A- like intragenic control region. Inspection of X. tropicalis, mouse and human U6 DNA upstream sequences revealed the presence of a TATA box as well as of the proximal and enhancer (octamer motif) elements contained in snRNA genes transcribed by RNA polymerase II. We propose that U6 RNAs are synthesized by a specialized transcription complex consisting of RNA polymerase III and transcription factors, some of which are very likely shared with RNA polymerase II promoters.
mesh_terms: D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004262:DNA Restriction Enzymes; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D005796:Genes; D011401:Promoter Regions, Genetic; D012319:RNA Polymerase II / Q000378:metabolism*; D012320:RNA Polymerase III / Q000378:metabolism*; D012342:RNA, Small Nuclear / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D014158:Transcription, Genetic; D014981:Xenopus
chemical_list: D012342:RNA, Small Nuclear; D012319:RNA Polymerase II; D012321:DNA-Directed RNA Polymerases; D012320:RNA Polymerase III; D004262:DNA Restriction Enzymes