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M9630713.TXT
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1996-02-27
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Document 0713
DOCN M9630713
TI Identification of ribozymes within a ribozyme library that efficiently
cleave a long substrate RNA.
DT 9603
AU Campbell TB; Cech TR; Howard Hughes Medical Institute, Department of
Chemistry and; Biochemistry, University of Colorado, Boulder 80309-0215,
USA.
SO RNA. 1995 Aug;1(6):598-609. Unique Identifier : AIDSLINE MED/96079988
AB Positions 2-6 of the substrate-binding internal guide sequence (IGS) of
the L-21 Sca I form of the Tetrahymena thermophila intron were
mutagenized to produce a GN5 IGS library. Ribozymes within the GN5
library capable of efficient cleavage of an 818-nt human
immunodeficiency virus type 1 vif-vpr RNA, at 37 degrees C, were
identified by ribozyme-catalyzed guanosine addition to the 3' cleavage
product. Three ribozymes (IGS = GGGGCU, GGCUCC, and GUGGCU) within the
GN5 library that actively cleaved the long substrate were characterized
kinetically and compared to the wild-type ribozyme (GGAGGG) and two
control ribozymes (GGAGUC and GGAGAU). The two control ribozymes have
specific sites within the long substrate, but were not identified during
screening of the library. Under single-turnover conditions, ribozymes
GGGGCU, GGCUCC, and GUGGCU cleaved the 818-nt substrate 4- to 200-fold
faster than control ribozymes. Short cognate substrates, which should be
structureless and therefore accessible to ribozyme binding, were cleaved
at similar rates by all ribozymes except GGGGCU, which showed a fourfold
rate enhancement. The rate of cleavage of long relative to short
substrate under single-turnover conditions suggests that GGCUCC and
GUGGCU were identified because of accessibility to their specific
cleavage sites within the long substrate (substrate-specific effects),
whereas GGGGCU was identified because of an enhanced rate of substrate
binding despite a less accessible site in the long substrate. Even
though screening was performed with 100-fold excess substrate (relative
to total ribozyme), the rate of multiple-turnover catalysis did not
contribute to identification of trans-cleaving ribozymes in the GN5
library.
DE Animal Base Sequence Binding Sites DNA Primers Molecular Sequence
Data RNA/*METABOLISM RNA, Catalytic/*METABOLISM RNA,
Protozoan/*METABOLISM Substrate Specificity Support, U.S. Gov't,
P.H.S. Tetrahymena JOURNAL ARTICLE
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).