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Summary: Research Focus
SR proteins: a foot on the exon before the transition
from intron to exon definition
Oren Ram and Gil Ast
Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978,
Israel
Two recent publications illuminate the evolution of
alternative splicing, showing that a SR (serine
arginine-rich) protein that regulates alternative splicing
in multicellular organisms is also found in a unicellular
organism without alternative splicing, in which it
can assist in the splicing of weak introns. Moreover,
insertion of SR proteins into an organism lacking such
proteins can restore the splicing of weak introns. These
results imply that SR proteins had already facilitated
the splicing of weak introns before the evolution of
alternative splicing.
Introduction
Introns are found in all eukaryotic organisms. However, the
number and size of introns and exons and their modes
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