Home Introduction Mechanism U1 U2 U4 U5
U6 References
Some Associated Proteins
(This
is not complete by any stretch of the imagination)
200 kDa
ATP-Binding Protein
Raghunathan and Guthrie showed that ATP and Brr2, a
DEIH-box ATPase, are essential in the disruption of the U4/U6
ribonucleoprotein complex (Raghunathan, 1998). They
immunopurified Brr2 in a native complex containing U1, U2, U5,
and U4/U6 snRNPs. When hydrolyzable ATP was added to this
complex, U4/U6 base-pairing was disrupted, and U4 and U6 snRNPs
were released. To test the necessity of Brr2, they used a mutated
Brr2 and saw that RNA rearrangements were prevented and splicing
didn’t occur. Thus, they concluded that ATP hydrolysis is
necessary and that the Brr2 is necessary for the unwinding event.
Dim1
Dim1 was discovered in 1997 by Berry et al. They induced several
different mutations in Dim1 and their analysis revealed that the
Dim1 protein was essential for entering mitosis and progressing
through the cell cycle (Berry et al, 1997). Zhang et al, in 2000,
conducted many two-hybrid screens and found that Dim1 is a
component of the U4/U6.U5 complex, and is required for pre-mRNA
splicing (Zhang et al, 2000).
The MUD2 protein was identified by Abovich et al in 1994 while screening mutant extracts of yeast for specific defects in the binding of U2 to pre-mRNA. They found that mutations in the MUD2 gene do not allow the binding of U2 to mRNA. This protein is in direct contact with the pre-mRNA and is a component of the pre-mRNA –U1 snRNP complex that commits the spliceosome to splice. Using genetic experiments, they showed that MUD2 affects U2 snRNP addition (Abovich et al, 1994).
Mud13p was identified by Colot et al in 1996. They isolated mutants that were lethal when combined with U1 snRNA mutants. They then screened the mutants that had indirect genetic interactions with the U1SnRNA mutations by a comparison of mutant extracts and in vitro commitment complex formation with wild type yeast. Colot et al found that Mud13p is a splicing factor that is a component of the commitment complex formed when U1 binds to pre-mRNA. Mud13p is a yeast homolog of the mammalian CBP20 (Colot et al, 1996).
P\PRP8
In
1998, Raghunathan and Guthrie showed that Prp24 is essential for
the annealing of U4 and U6 complexes (Raghunathan et al. 1998).
They immunodepleted >97% epitope-tagged Prp24 from yeast
extract. They found that when visualized by native-gel
electrophoresis, splicing generated free U4 and U6 SnRNPs and
almost all U4/U6.U5 and U4/U6 snRNPs disappeared. When
Prpr24 protein from yeast was added, they saw free U4 was
diminished, U6 was no longer present, and U4/U6 and
U4/U6.U5 snRNPs were restored
In 1998, Gross et al isolated the Srp1 protein which plays a role
in suppressing pre-mRNA splicing. They showed that overexpression
of the RNA binding domain of Srp1 causes accumulation of
pre-mRNA, which correlates with cessation of growth and loss of
splicing activity (Gross et al, 1998).
Sub2p
Sub2p was discovered in 2001 by Zhang et al. They found that it was essential for pre-mRNA splicing because it is needed for the formation of the commitment complex in which U1 binds to pre-mRNA. This research team concluded that the Sub2p in conjunction with the Prp5p protein assist in controlling the U2 snRNP-branchpoint interaction (Zhang et al, 2001).