Volume 270,
Number 22,
Issue of June 2, pp. 13415-13421, 1995
©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
A
Mammalian Activity Required for the Second Step of Pre-messenger RNA
Splicing
Laura A.
Lindsey
,
Allen J.
Crow
,
Mariano
A.
Garcia-Blanco
Splicing of precursors to messenger RNAs occurs via a two-step
mechanism. In the first step, the 5`-exon is released concomitant with
the production of a lariat intermediate, and in the second step, the
exons are joined, releasing the intron in the form of a lariat product.
Several gene products of the yeast Saccharomyces cerevisiae have been shown to be required exclusively for the second step.
Although mammalian proteins have been implicated in the second step of
splicing, none have been shown to act only at this step. We identify
here the first mammalian activity shown to be exclusively required for
the second step. The activity was shown to increase by 5-fold the rate
for this splicing step, whereas it had no effect on the rate of the
first step. The activity was not affected by treatment with micrococcal
nuclease, whereas it is sensitive to heating to 55 °C, suggesting
that it is not dependent on an RNA, but more likely is a protein. The
second step activity was separated from other factors required for the
first step and from PSF, a splicing factor thought to have a second
step activity. The activity does not require ATP hydrolysis, suggesting
that it acts at a late stage of the second step of splicing.
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