Rt. Okeefe et al., THE INVARIANT U5 SNRNA LOOP-1 SEQUENCE IS DISPENSABLE FOR THE FIRST CATALYTIC STEP OF PRE-MESSENGER-RNA SPLICING IN YEAST, Cell, 86(4), 1996, pp. 679-689
We have developed an in vitro reconstitution system to investigate the
role of U5 snRNA in the two catalytic steps of pre-mRNA splicing. The
invariant U5 loop 1 is known to interact with exon sequences at the 5
' splice site before the first catalytic step. Remarkably, analysis of
U5 mutations in vitro reveals that the first transesterification occu
rs accurately in the absence of the U5 loop. Therefore this sequence i
s not an essential component of the spliceosomal active site for the f
irst catalytic step. The second catalytic step, although strongly depe
ndent on the presence of a U5 loop to tether the exon 1 splicing inter
mediate, is surprisingly tolerant of mutations in the invariant sequen
ce.