For such an apparently well-understood molecule, it's certainly taken enough time for RNA to become a focus of drug discovery. But increasingly, it's the new, hot target. Companies focusing on or around RNA are multiplying. One of the best funded of the new companies is PTC Therapeutics, with $56 million raised so far. PTC is creating a platform around the post-transcriptional modulation of RNA, aiming to increase or decrease gene expression by tinkering with the mechanics of how RNA makes proteins.