Eukaryotic genome promoter region

In eukaryotic genomes, DNA transcription control elements may be located many kilobases away from the promoter they regulate. Different control regions can control transcription of the same gene in different cell types. 

Much of the eukaryotic genome is noncoding, although a large proportion of it is still transcribed. The promoter regions, which are characteristically more A-T rich and much larger than their prokaryotic equivalents, are not transcribed, so this can alter the base composition of the transcriptome relative to the genome. 

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