A U.S. District Court has ruled that F. Hoffmann-La Roche Ltd.'s U.S. patent covering native Thermus Aquaticus (Taq) DNA polymerase is unenforceable and therefore in the public domain. But the pharma company maintains that the decision has little bearing on its PCR franchise, becuase the enzyme is predominantly sold in recombinant forms.

The ruling comes in a suit brought by Roche against Promega Corp. in the U.S. District Court for the Northern District of California, alleging breach of contract for the sale of Taq and patent infringement. Promega (Madison, Wis.) counterclaimed, saying that Roche's U.S. Patent No. 4,889,818 covering native Taq, a thermostable enzyme used in gene sequencing as well as in PCR, was obtained fraudulently and therefore unenforceable.