Structure of Long Telomeric RNA Transcripts: THE G-RICH RNA FORMS A COMPACT REPEATING STRUCTURE CONTAINING G-QUARTETS*

AUTOR(ES)
FONTE

American Society for Biochemistry and Molecular Biology

RESUMO

Recent studies have identified RNA transcripts arising from mammalian telomeres with the transcript of the C-rich strand (r(5′-UUAGGG-3′)n) being much more abundant than transcripts of the G-rich strand. Here we used transmission electron microscopy, CD, and nuclease digestion to investigate the structure of ∼640-nucleotide (nt) RNA transcripts of the C-rich and G-rich strands of mammalian telomeric DNA. The CD spectrum of the C-rich RNA in low salt (10 mm KCl) or high salt (100 mm KCl) was typical of mixed sequence RNA, whereas the CD spectrum for the G-rich RNA differed with changes characteristic of parallel G-quadruplexes at the higher salt concentration. Electron microscopy visualization of the C-rich RNA revealed relatively extended unstructured molecules 59.7 ± 17.8 nm in length and with a width consistent with single-stranded RNA following metal coating. In contrast, the G-rich RNA was observed as round particles and short, thick rods with the rods being most prevalent in high salt conditions and absent in low salt. The rods were 22.7 ± 4.8 nm in length and 7.6 nm in width. Digestion of the G-rich RNA with T1 RNA nuclease revealed a ladder of bands whose sizes were integral multiples of 24 nt plus a 4-nt overhang. These observations suggest a model in which G-rich telomeric RNA folds into chains of particles each consisting of four (UUAGGG) repeats stabilized by parallel G-quartets and joined by UUA linkers. These chains further condense to form short rods and round particles.

ACESSO AO ARTIGO

Documentos Relacionados