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Mol. Cell. Biol., Dec 1997, 7178-7185, Vol 17, No. 12
Q Huang, MR Jacobson and T Pederson
The spliceosomal small nuclear RNAs U1, U2, U4, and U5 are transcribed by
RNA polymerase II as precursors with extensions at their 3' ends. The 3'
processing of these pre-snRNAs is not understood in detail. Two pathways of
pre-U2 RNA 3' processing in vitro were revealed in the present
investigation by using a series of human wild-type and mutant pre-U2 RNAs.
Substrates with wild-type 3' ends were initially shortened by three or four
nucleotides (which is the first step in vivo), and the correct mature 3'
end was then rapidly generated. In contrast, certain mutant pre-U2 RNAs
displayed an aberrant 3' processing pathway typified by the persistence of
intermediates representing cleavage at each internucleoside bond in the
precursor 3' extension. Comparison of the wild-type and mutant pre-U2 RNAs
revealed a potential base-pairing interaction between nucleotides in the
precursor 3' extension and a sequence located between the Sm domain and
stem-loop III of U2 RNA. Substrate processing competition experiments using
a highly purified pre-U2 RNA 3' processing activity suggested that only
RNAs capable of this base-pairing interaction had high affinity for the
pre-U2 RNA 3' processing enzyme. The importance of this postulated
base-pairing interaction between the precursor 3' extension and the
internal region between the Sm domain and stem-loop III was confirmed by
the results obtained with a compensatory substitution that restores the
base pairing, which displayed the normal 3' processing reaction. These
results implicate a precursor-specific base-paired structure involving
sequences on both sides of the mature cleavage site in the 3' processing of
human U2 RNA.
Copyright © 1997, American Society for Microbiology
3' processing of human pre-U2 small nuclear RNA: a base-pairing interaction between the 3' extension of the precursor and an internal region
Cell Biology Group, Worcester Foundation for Biomedical Research, Shrewsbury, Massachusetts 01545, USA.
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