Genome complexity: making immune proteins (Introduction)

by David Turell , Monday, December 29, 2014, 14:39 (3621 days ago) @ David Turell

Creating antibodies to fight infections is a huge job, as there are so many different pathogens. It involves snipping DNA and recombining it precisely:-"The immune system relies on the formation of specialized proteins (antibodies) that can recognize and immobilize foreign invaders like viruses and bacteria. Since storing individual blueprints for each of these proteins would require huge amounts of DNA, the body instead mixes and matches different chunks of sequence to produce roughly 300 trillion possibilities. This mixing and matching, called recombination, requires that DNA be clipped by the enzyme RAG.-"Recombination is essential for the immune system's ability to recognize and fight new enemies, but too much clipping can cause harmful chromosome rearrangements," says Stephen Desiderio, M.D., Ph.D., director of the Institute for Basic Biomedical Sciences and the senior researcher for the study. "We now know that RAG has a built-in lock that prevents it from getting out of hand as it clips DNA."-"To keep the system efficient, each immune cell makes only a single antibody and only does so after being activated. Several years ago, Desiderio's group found that this level of control is enforced by a segment of RAG called the PHD. The PHD binds to a chemical tag called H3K4me3, which is only found on DNA that is actively being rewritten as RNA. This prevents RAG from recombining DNA that is not active."-
 Read more at: http://phys.org/news/2014-12-mechanism-scissors-dna.html#jCp-Note to dhw: this is how immune cells are sentient and react, by precise molecular action. All evolved by what random process?!