TY - JOUR
T1 - Can GC content at third-codon positions be used as a proxy for isochore composition?
AU - Elhaik, Eran
AU - Landan, Giddy
AU - Graur, Dan
PY - 2009/8
Y1 - 2009/8
N2 - The isochore theory depicts the genomes of warm-blooded vertebrates as a mosaic of long genomic regions that are characterized by relatively homogeneous GC content. In the absence of genomic data, the GC content at third-codon positions of protein-coding genes (GC3) was commonly used as a proxy for the GC content of isochores. Oddly, in the postgenomic era, GC3 is still sometimes used as a proxy for the GC composition of isochores. Here, we use genic and genomic sequences from human, chimpanzee, cow, mouse, rat, chicken, and zebrafish to show that GC3 only explains a very small proportion of the variation in GC content of long genomic sequences flanking the genes (GCf), and what little correlation there is between GC3 and GCf was found to decay rapidly with distance from the gene. The coefficient of variation of GC3 was found to be much larger than that of GCf and, therefore, GC3 and GCf values are not comparable with each other. Comparisons of orthologous gene pairs from 1) human and chimpanzee and 2) mouse and rat show strong correlations between their GC3 values, but very weak correlations between their GCf values. We conclude that the GC content of third-codon position cannot be used as stand-in for isochoric composition. The Author 2009.
AB - The isochore theory depicts the genomes of warm-blooded vertebrates as a mosaic of long genomic regions that are characterized by relatively homogeneous GC content. In the absence of genomic data, the GC content at third-codon positions of protein-coding genes (GC3) was commonly used as a proxy for the GC content of isochores. Oddly, in the postgenomic era, GC3 is still sometimes used as a proxy for the GC composition of isochores. Here, we use genic and genomic sequences from human, chimpanzee, cow, mouse, rat, chicken, and zebrafish to show that GC3 only explains a very small proportion of the variation in GC content of long genomic sequences flanking the genes (GCf), and what little correlation there is between GC3 and GCf was found to decay rapidly with distance from the gene. The coefficient of variation of GC3 was found to be much larger than that of GCf and, therefore, GC3 and GCf values are not comparable with each other. Comparisons of orthologous gene pairs from 1) human and chimpanzee and 2) mouse and rat show strong correlations between their GC3 values, but very weak correlations between their GCf values. We conclude that the GC content of third-codon position cannot be used as stand-in for isochoric composition. The Author 2009.
KW - Compositional patterns
KW - Flanking regions
KW - GC content
KW - GC3
KW - Genome composition
KW - Isochores
UR - http://www.scopus.com/inward/record.url?scp=67749124224&partnerID=8YFLogxK
U2 - 10.1093/molbev/msp100
DO - 10.1093/molbev/msp100
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AN - SCOPUS:67749124224
SN - 0737-4038
VL - 26
SP - 1829
EP - 1833
JO - Molecular Biology and Evolution
JF - Molecular Biology and Evolution
IS - 8
ER -