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Introduction Most RNA-polymerase-II transcripts of higher eukaryotes are

Summary: Introduction
Most RNA-polymerase-II transcripts of higher eukaryotes are
synthesized as precursor mRNA (pre-mRNA) containing exons
and introns. During the splicing reaction, introns are removed
and exons are ligated to form an mRNA, which is transported
to the cytoplasm and translated to form a protein (Burge et al.,
1999; Jurica and Moore, 2003; Rappsilber et al., 2002). Four
short degenerate sequences are essential for splicing; the 5 and
3 splice sites (5ss and 3ss) (GU and AG, respectively) located
at the 5 and 3 ends of the intron, and the polypyrimidine tract
and branch-site sequence, which are located upstream of the
3ss (Brow, 2002). Alternative splicing, in which different
subsets of exons or splice sites in a given pre-mRNA are
chosen, is a major mechanism that diversifies the genetic
information by producing more than one type of mRNA from
a single gene (Graveley, 2001). Exon choice is determined by
different nuclear protein concentrations that vary among
tissues (Hanamura et al., 1998) and cell types (Jensen et al.,
2000) or during development (Lallena et al., 2002; Mahe et al.,
2000; Smith and Valcarcel, 2000; Wang and Manley, 1995),


Source: Ast, Gil - Department of Molecular Genetics and Biochemistry, Tel Aviv University


Collections: Biology and Medicine