The '516 patent relates to the regulation of gene expression by the transcription factor NF-[K]B. The inventors were the first to identify NF-[K]B and to uncover the mechanism by which NF-[K]B activates gene expression underlying the body's immune responses to infection. NF-[K]B was found to normally exists in cells as an inactive complex with a protein inhibitor, named 'I[K]B' ('Inhibitor of kappa B'), and is activated by extracellular stimuli, such as bacterial-produced lipopolysaccharides, through a series of biochemical reactions that release it from I[K]B. Once free of its inhibitor, NF-[K]B travels into the cell nucleus where it binds to and activates the transcription of genes containing a NF-[K]B recognition site. The activated genes (e.g., certain cytokines), in turn, help the body to counteract the extracellular assault. The inventors realized that artificially interfering with NF-[K]B activity could reduce the harmful symptoms of certain diseases, and they filed a patent application on April 21, 1989, disclosing their discoveries and claiming methods for regulating cellular responses to external stimuli by reducing NF-[K]B activity in a cell. Ariad (P) sued Lilly (D) the day the '516 patent issued. The jury rendered a special verdict finding infringement and it also found that the asserted claims were not invalid for anticipation, lack of enablement, or lack of written description. On appeal, a panel of the court reversed the district court's denial of D's motion for judgment as a matter of law (JMOL) and held the asserted claims invalid for lack of written description. P petitioned for rehearing en banc disputing the interpretation of 35 U.S.C. § 112, first paragraph, as containing a separate written description requirement separate from the enablement requirement and, if so, the scope and purpose of that requirement.