SAN FRANCISCO -- A federal judge here on Tuesday afternoonrejected Cetus Corp.'s requests for a directed verdict regardingsix patent claims -- disputed by Du Pont -- for polymerasechain reaction (PCR) technology.

No further details were immediately available concerning theruling by U.S. District Court Judge Marilyn Hall Patel, who ispresiding over the closely followed patent infringement trial.The potentially lucrative technology can produce billions ofcopies of a gene sequence in a matter of hours.

Du Pont sued Cetus in 1989, seeking to have two Cetus patentsfor PCR ruled invalid on the grounds that the PCR inventionwas obvious, based on two key scientific papers published inthe early 1970s. Cetus countersued Du Pont last year, alleginginfringement of its patents.

Cetus contended in its recent motion that the six claims shouldnot be subject to the trial because Du Pont did not presentsufficient relevant evidence to support its case. The six claimswere from U.S. Patent 4,683,202, claims 11, 12, 13 and 15; andfrom U.S.P. 4,683,195, claims 5 and 9.

Patel last November rejected Du Pont's motion for a summaryjudgment that the Cetus patents were invalid.

Cetus is selling PCR equipment and reagents under theGeneAmp trade mark in partnership with Perkin-Elmer Corp.Hoffmann-La Roche Inc. of Nutley, N.J., is a partner on PCRapplications for human diagnostic products.

Du Pont last March started selling its own DNA polymerase, PCRprimer and reagent kits.

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