After receiving his doctorate, Mullis briefly left science to write fiction before accepting the University of Kansas fellowship. During his postdoctoral work, he managed a bakery for two years. Mullis returned to science at the encouragement of Berkeley friend and colleague Thomas White, who secured Mullis' UCSF position and later helped Mullis land a position with the biotechnology company Cetus Corporation of Emeryville, California. Despite little experience in molecular biology, Mullis worked as a DNA chemist at Cetus for seven years, ultimately serving as head of the DNA synthesis lab under White, then the firm's director of molecular and biological research; it was there, in 1983, that Mullis invented the polymerase chain reaction.