Strange protein-based parasite helps tuberculosis survive immune assault

Occasionally, there are research findings that aren't especially exciting but provide a great opportunity to provide a glimpse into fascinating areas of science. This week, PNAS was kind enough to provide one. It's a nice paper about how what you might call a "molecular parasite" was adopted by one of its hosts and turned into a useful tool. But really, it's an excuse to delve into the world of molecular parasites.

Mostly, we think of parasites as individual organisms that get free rides from their hosts, living in or on them and draining off nutrients. But that definition can also apply to some things that aren't organisms, never really leave the cell, and are little more than stretches of DNA. They're often called molecular parasites to distinguish them from the more traditional variety.

Types of parasites

The most widespread examples of these are called transposons, the mobile DNA first discovered by Nobel winner Barbara McClintock. These are stretches of DNA that encode proteins that help them move around the genome. The proteins recognize the transposon ends and can either make a new copy of the DNA or chop the existing one out of its current location. Once a free copy is available, the proteins can move it to a new location. They're so effective at this that roughly 40 percent of most mammalian genomes (including our own) are random bits and pieces of transposons.