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2009NatureAmerica,Inc.Allrightsreserved. nature structural & molecular biology advance online publication

Summary: 2009NatureAmerica,Inc.Allrightsreserved.
nature structural & molecular biology advance online publication
ana lys i s
Mammalian genomes are packaged together with histone proteins in
the form of chromatin. The intertwined DNA harbors genes, most of
which are made up of short stretches of exonic sequences interrupted
by long noncoding introns. This organization imposes two distinct
code sets: the splicing code and the chromatin code (nucleosome
occupancy). The splicing code, which comprises a set of four signals
at the exon-intron junctions and a vast array of splicing regulatory
elements (SREs), directs the spliceosomal machinery to the exon-
intron boundaries, allowing precise identification of exons14. Despite
decades of research, the factors allowing differentiation of exons from
long flanking introns are far from understood, especially for `higher'
eukaryotes. Although exon lengths in these organisms seem to be
under strong evolutionary pressure to remain within a constant range
of ~140 nucleotides (nt)5, introns have expanded to several thousands
of nucleotides in length, and their length does not seem to be under
evolutionary selection.
DNA sequence modulates how and where the DNA is packaged


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


Collections: Biology and Medicine