Abstract
The human genome, as the genome of all mammals and birds, are mosaic of isochores, which are very long streches (>> 100 kb) of DNA that are homogeneous in base composition. Isochores can be divided in a small number of families that cover a broad range of GC levels (GC is the molar ratio of guanine+cytosine in DNA). In the human genome, we fi nd fi ve families, which are (going from GCpoor to GC- rich) L1, L2, H1, H2 and H3. This organization has important consequences, as is the case of the concentration of genes, their regulation, transcription levels, rate of recombination, time of replication, etc. Furthermore, the existence of isochores has as a consequence the so called “compositional correlations”, which means that as long as sequences are placed in diff erent families of isochores, all of their regions (exons and their three codon positions, introns, etc.) change their GC content, and as a consequence, both codon and amino acids usage change in each isochore family. Finally, we discuss the origin of isochores within an evolutioary framework.
Highlights
The human genome, as the genome of all mammals and birds, are mosaic of isochores, which are very long streches (>> 100 kb) of DNA that are homogeneous in base composition
In the human genome, we find five families, which are (going from GCpoor to GC- rich) L1, L2, H1, H2 and H3
The evolution of isochore patterns in vertebrate genomes
Summary
Resumen: El genoma humano, como el de todos los mamíferos y aves, es un mosaico de isocoros, los que son regiones muy largas de ADN (>> 100 kb) que son homogéneas en cuanto a su composición de bases. Los isocoros pueden ser divididos en un pequeño número de familias que cubren un amplio rango de niveles de GC (GC es la relación molar de guanina+citosina en el ADN). La existencia de los isocoros lleva a las llamadas “correlaciones composicionales”, lo que significa que en la medida en que diferentes secuencias están localizadas en diferentes isocoros, todas sus regiones (exones y sus tres posiciones de los codones, intrones, etc.) cambian su contenido en GC, y como consecuencia, cambian tanto el uso de aminoácidos como de codones sinónimos en cada familia de isocoros. Palabras clave: Genoma humano, isocoros, correlaciones composicionales, contenido en GC, evolución
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