GC characterization within and among isochores in mammalian genomes by CsCl and sequence analyses

What is it about?

We addressed the quantitative characterization of the compositional heterogeneity of genomes, as measured by the GC distributions of fixed-length fragments. Special attention was given to mammalian genomes, since their compartmentalization into isochores implies two levels of heterogeneity, intra-isochore (local) and inter-isochore (global). This partitioning is a natural one, since large-scale compositional properties vary much more among isochores than within them. Intra-isochore GC distributions become roughly Gaussian for long fragments, and their standard deviations decrease only slowly with increasing fragment length, unlike random sequences. This effect can be explained by 'long-range' correlations along isochores.

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Why is it important?

The distribution of GC level along nuclear genomes, or along one of its compositional fractions, encodes key information on their structural, functional properties and evolution, which can be inferred either from absorbance profiles of the DNA in CsCl density gradients at sedimentation equilibrium, or by scanning long contigs of largely sequenced genomes.

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