Arthur L. Horwich (born 1951) is an American biologist and Sterling Professor of Genetics and Pediatrics at the Yale School of Medicine.

"[10] In 1981, Horwich moved back to New Haven, Connecticut for a postdoctoral fellowship at Yale University School of Medicine.

As an independent researcher, Horwich asked whether the pathway that imports an enzyme called ornithine transcarbamylase (OTC) into the mitochondria of mammalian cells also could work in yeast.

In 1987, during a genetic screen in yeast, Horwich and his colleagues stumbled across a protein folding function inside mitochondria.

Such assemblies, known as chaperonins, also exist in other cellular compartments and are essential components, mediating protein folding under both heat shock and normal conditions.

They and others found early on that a chaperonin-mediated folding reaction can be reconstituted in a test tube, and that has enabled structural and functional studies that have begun to explain how chaperonins work.