Solution: Protein shell of a virus - NYT Crossword

This was one of those bits of knowledge that you’ve either got in that mind of yours or you don’t. It’s appeared once before in the puzzle, similarly clued, as a set of proteins that form a protective coat around the genetic material in a virus: a CAPSID. It’s actually pretty vital; without it, that genetic material can work only inside a host cell, as a viroid, apparently unable to replicate and infect animals at all, just plants. Still simpler, though, are prions — remember them? They’re behind mad cow disease, and its outbreak in the ‘90s that led to an eye-opening reveal of our livestock practices, like a modern version of “The Jungle.”