RNA B is the major nucleolar trimethylguanosine-capped small nuclear RNA associated with fibrillarin and pre-rRNAs in Trypanosoma brucei.
RNA B is one of three abundant trimethylguanosine-capped U small nuclear RNAs (snRNAs) of Trypanosoma brucei which is not strongly identified with other U snRNAs by sequence homology. We show here that RNA B is a highly diverged U3 snRNA homolog likely involved in pre-rRNA processing. Sequence identity between RNA B and U3 snRNAs is limited; only two of four boxes of homology conserved between U3 snRNAs are obvious in RNA B. These are the box A homology, specific for U3 snRNAs, and the box C homology, common to nucleolar snRNAs and required for association with the nucleolar protein, fibrillarin. A 35-kDa T. brucei fibrillarin homolog was identified by using an anti-Physarum fibrillarin monoclonal antibody. RNA B and fibrillarin were localized in nucleolar fractions of the nucleus which contained pre-rRNAs and did not contain nucleoplasmic snRNAs. Fibrillarin and RNA B were precipitated by scleroderma patient serum S4, which reacts with fibrillarins from diverse organisms; RNA B was the only trimethylguanosine-capped RNA precipitated. Furthermore, RNA B sedimented with pre-rRNAs in nondenaturing sucrose gradients, similarly to U3 and other nucleolar snRNAs, suggesting that RNA B is hydrogen bonded to rRNA intermediates and might be involved in their processing.
Hartshorne
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T
Intercampus Program in Molecular Parasitology, School of Pharmacy, University of California, San Francisco 94143-1204.
Agabian
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N
D000818:Animals; D001483:Base Sequence; D002451:Cell Compartmentation; D002466:Cell Nucleolus / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009694:Nucleic Acid Precursors / Q000235:genetics; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D011233:Precipitin Tests; D012315:RNA Caps / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D016053:RNA, Protozoan / Q000235:genetics*; D012335:RNA, Ribosomal / Q000235:genetics; D012342:RNA, Small Nuclear / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000235:genetics*
D002868:Chromosomal Proteins, Non-Histone; D009694:Nucleic Acid Precursors; D009838:Oligodeoxyribonucleotides; D012315:RNA Caps; D016053:RNA, Protozoan; D012335:RNA, Ribosomal; D012342:RNA, Small Nuclear; C047458:fibrillarin