Nucleic Acids Research, Vol 26, Issue 24 5699-5706, Copyright © 1998 by Oxford University Press
B Pan, SN Mitra, L Sun, D Hart and M Sundaralingam
The crystal structure of the RNA octamer duplex r(CCCIUGGG)2has been
elucidated at 2.5 A resolution. The crystals belong to the space group
P21and have unit cell constants a = 33.44 A, b = 43.41 A, c = 49.39 A and
beta = 104.7 degrees with three independent duplexes (duplexes 1-3) in the
asymmetric unit. The structure was solved by the molecular replacement
method and refined to an Rwork/Rfree of 0.185/0.243 using 3765 reflections
between 8.0 and 2.5 A. This is the first report of an RNA crystal structure
incorporating I.U wobbles and three molecules in the asymmetric unit.
Duplex 1 displays a kink of 24 degrees between the mismatch sites, while
duplexes 2 and 3 have two kinks each of 19 degrees and 27 degrees, and 24
degrees and 29 degrees, respectively, on either side of the tandem
mismatches. At the I.U/U.I mismatch steps, duplex 1 has a twist angle of
33.9 degrees, close to the average for all base pair steps, but duplexes 2
and 3 are underwound, with twist angles of 24.4 degrees and 26.5 degrees,
respectively. The tandem I.U wobbles show intrastrand purine-pyrimidine
stacking but exhibit interstrand purine-purine stacking with the flanking
C.G pairs. The three independent duplexes are stacked non-coaxially in a
head-to-tail fashion to form infinite pseudo-continuous helical columns
which form intercolumn hydrogen bonding interactions through the
2'-hydroxyl groups where the minor grooves come together.
ARTICLES
Crystal structure of an RNA octamer duplex r(CCCIUGGG)2 incorporating tandem I.U wobbles
Department of Chemistry and Department of Biochemistry and Biophysics Program, The Ohio State University,Biological Macromolecular Structure Center, Columbus, OH 43210, USA.
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