by Alan Der­man — Imag­ine try­ing to ac­quaint your­self with your fa­vorite bac­terium by learn­ing the in­tra­cel­lu­lar ad­dress of each and every one of its pro­teins. You can't see them in a light mi­cro­scope, and you can't re­al­is­ti­cally do im­muno­flu­o­res­cence; for that you'd need to pu­rify each one and raise an­ti­bod­ies. So you have to mod­ify them so that they can be seen. You have to tag them with...