Final answer:
François Jacob and Jacques Monod hypothesized the existence of messenger RNA (mRNA), a key intermediary in the process of translating genetic information from DNA into proteins.
Step-by-step explanation:
In 1961, the French scientists François Jacob and Jacques Monod hypothesized the existence of messenger RNA (mRNA), an intermediary molecule between DNA and its protein products. Their hypothesis suggested that DNA contains the full library of cellular information, and mRNA acts as a temporary photocopy of the specific information necessary for the synthesis of proteins at a given time, which is delivered to the ribosome. This discovery was pivotal in understanding gene expression and regulation, particularly their work on the lac operon in E. coli, which demonstrated how genes could be controlled together through a set of genes transcribed as a single mRNA strand.