François Jacob is known as one of the key figures in the history of molecular biology. His elaboration, together with Jacques Monod, of the operon model and the basic features of the regulation of gene expression in bacteria, as well as the concept of genetic messenger, won him the Nobel Prize in 1965. Both notions were decisive for the novel imagery of molecular genetics in which the notion of information came to stand central. From a close reading, this article tries (...) to reconstruct how the new language of molecular genetics took shape in the scientific writings of Jacob. In particular, it analyzes how the notions of regulation, information, and language came to be articulated, and how this articulation changed and underwent modulations over time. It shows that a scientific language consists of several layers and thus, as a rule, forms a hybrid structure. The time span covered reaches from the early experiments done together with Monod and Arthur Pardee between 1958 and 1960, also known as the “PaJaMo” experiment, to Jacob’s book on the history of heredity, The Logic of Life, which appeared in 1970. (shrink)