In the chapter called THE RIDDLE OF THE 1.6% I explain how relatively small differences between chimps and humans at the level of DNA nucleotide sequence in genes can be tremendously amplified by a variety of mechanisms that change how hard a gene works - and when - and therefore how much protein it produces. Lisa Stubbs and Katja Nowick, from the University of Illinois, have just provided important and specific evidence for how this can come about. It has been understood for some time that some genes act as master controllers of an orchestra of subservient genes because they produce proteins called transcription factors that attach to a large number of genes and either ramp up or reduce their activity. These gene expression differences are particularly pronounced in the human brain, versus that of the chimpanzee and are involved in various processes that supply energy sources to the greedy human brain or are involved in building larger and longer synapse networks etc. etc. As Stubbs says, "These differences fit what we know because the human brain is so much larger and proteins need to be shuttled a long way out to the synapses. A higher requirement for metabolic energy has also been demonstrated independently for human brains."
The duo looked at a family of transcription factors known as the KRAB zinc finger genes and discovered 90 transcription factors that were implicated in the activity of 1000 genes - causing an upsurge of activity in the human brain. "Once this network of transcription factors is established, changes in the network can be amplified because transcription factors control other genes", says Nowick, "even a small change in transcription factor expression can therefore produce a large effect on overall gene expression differences between chimpanzees and humans." Stubbs adds that: "Our very strong bias is to believe that these transcription factors are involved in speciation and traits that make species unique"
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