The lawsuit alleges that GE Healthcare's CyScript reverse transcriptase enzymes and kits infringe on six patents. Although four of these expired earlier this year, Invitrogen is seeking royalties on past sales of GE products. Should Invitrogen successfully argue that GE Healthcare had wilfully infringed the patents, the firm would be entitled to triple damages. The US patents at the centre of the debate are Nos. 6,610,522; 6,589,768; 6,063,608 and 5,668,005, which all expired in January this year. Patents 5,244,797 and 5,405,776 are similar, relating to a gene which encodes reverse transcriptase having DNA polymerase activity and substantially no RNase H activity. The invention also relates to vectors containing the gene and hosts transformed with the vectors of the invention. The invention details a method of producing reverse transcriptase having DNA polymerase activity and substantially no RNase H activity by expressing the reverse transcriptase genes of the present invention in a host. It also relates to a method of producing cDNA from mRNA using the reverse transcriptase of the invention. The kit for the preparation of cDNA from mRNA comprises the reverse transcriptase of the invention. Invitrogen has been at the centre of much legal squabbling concerning tools used in complementary DNA synthesis, polymerase chain reaction (PCR) and other molecular biology applications. In February of this year. Invitrogen and Agilent finally settled patent infringement in which Agilent agreed to make an undisclosed payment to Invitrogen. In return, Agilent had to stop sale of its RNase H minus reverse transcriptase products. Invitrogen also had to take out a license from Agilent for its DNA polymerase blend products and pay royalty fees, also undisclosed. Exactly how much a patent can restrict research conducted by another company is a question that is certain to affect the way innovative new drugs are researched and developed. As far back as April 2005, Invitrogen has insisted that its $26bn research tool industry would go bankrupt if rival companies are given freedom to tinker with their patented work without paying a licensing fee first. "The patent system, as it presently operates, provides the incentive necessary to fuel the development of innovative and beneficial research tools by granting an inventor the exclusive right to control the use of his invention for a limited time," Invitrogen stated.