Virology Lectures 2017 #24: Unusual Infectious Agents

What is the smallest genome that can sustain an infectious agent? Might the genome of an infectious agent encode no protein? Could an infectious agent exist without a genome? These questions are answered by the amazing viroids - small RNAs that encode no proteins - satellites, and prions - infectious proteins that cause diseases like Creutzfeldt-Jakob and bovine spongiform encephalopathy, or mad cow disease.