The X Man

[IMT staff]

The real answer is the activity of a protein complex that, like a genetic power tool, gives enzymes on the X-chromosome an extra boost to increase gene expression.

Women have two X-chromosomes in their genomes while males have an X and a Y. Gender is defined by that difference, but for men to live, the genetic imbalance must be remedied. In mammals, cells therefore work to emphasize, or "upregulate," the lone X-chromosome in males and de-emphasize, or "downregulate," the extra X-chromosome in females.

Scientists already suspected that X-chromosome upregulation had a lot to do with a protein complex called MSL that binds to the X-chromosome. MSL stands for "male-specific lethal" because the mutant form would prove deadly for a male fruitfly. What scientists didn't know was how it worked. It's not easy to double the levels of expression of a wide variety of genes on one specific chromosome.

The X Man - Blog - Testosterone replacement & general men's health articles

 

[Mr P]

Researchers used a technique called "global run-on sequencing" to measure how much of an enzyme called RNA polymerase II was active in the X-chromosome. RNA polymerase II converts DNA instructions into RNA code to express genes. They found that all chromosomes have the same amount of the enzyme, to a point. After that - farther along each gene - the X-chromosome has noticeably more than other chromosomes. In other words, something allows more RNA polymerase II to move farther along the X-chromosome genes, past the point where those enzymes start to peter out on other chromosomes.

this ^^ is very interesting stuff