How a virus ancestor powers our memory’s chemistry

Since its discovery in 1995, a protein called Arc has gradually revealed long-sought secrets about how memory works – but by 2013, Jason Shepherd was ‘a little bored’ of it. He’d worked on Arc since his undergraduate studies in 2001. By 2013, when he founded his current lab at the University of Utah, US, he thought ‘we’ve figured out most of what it does’. But within five years Shepherd’s team published what he called a ‘completely unexpected’ finding in the version of Arc that mammals like us have. At the same time, Vivian Budnik’s group at the University of Massachusetts, US, published a similar finding for the version of Arc found in flies.

In 2018, both teams showed that Arc can form itself into a capsid shell similar to a virus’s, and carry RNA genetic information between cells. This awesome idea surprised scientists in part because they didn’t have a full picture of Arc’s structure, and still don’t for the mammalian version. ‘The structure can give you a clue,’ Shepherd tells Chemistry World. ‘Which parts are sticking out of and into the capsid could determine the cargo.’ The findings reinforced an earlier suggestion that, millions of years ago, complex life forms found a way to use an ancestor of modern retroviruses like HIV to help us think.