Swiss drugmaker Roche said it has entered a deal worth up to $1 billion with Alnylam Pharmaceuticals to gain access to the Cambridge, MA-based firm’s skills in RNA interference (RNAi) technology.

Under the deal, Roche will pay Alnylam $331 million upfront in cash and equity investment. Future payments will be made upon reaching certain milestones.

The deal also makes Roche a co-investor in Alnylam, along with Swiss rival Novartis, which purchased a 19.9% stake in Alnylam in 2005.

Last month, Alnylam said it had begun a Phase II clinical trial of ALN-RSV01 to treat respiratory syncytial virus that infects the upper and lower respiratory tract, usually in children and people with weak immune systems.

RNAi is considered one of the hottest areas in biotechnology research and was the basis for last year’s Nobel Prize in medicine. It is seen as having potential to produce promising treatments for cancer, blindness and AIDS.

Last October, Merck paid $1.1 billion for RNAi technology-based treatment development firm Sirna Therapeutics. Since then, other drugmakers including Pfizer, have struck a series of RNAi product development deals.