This is the second deal in the past week in which a big drugmaker has agreed to plunk down a lot of change for RNA interference, or RNAi, one of the hottest areas of drug research. Last week, AstraZeneca agreed to pay $405 million to Since Therapeutics and last year, Merck paid $1.1 billion to buy Sirna Therapeutics.

Roche, however, will pay Alnylam $331 million upfront, including a cash payment and an equity investment of $42.5 million, and that amounts to less than 5 percent of Alnylam’s outstanding shares.

RNAi represents a breakthrough in understanding how genes can be silenced, and was the basis for last year’s Nobel prize in medicine. The ability to turn genes on or off could provide a new way to treat many diseases. Although Denise Anderson, an analyst with Kepler Equities, told Reuters that Roche was paying a high price, given that the drug research is still early-stage and the market capitalization of Alnylam is less than $600 million.

Lee Babiss, Roche’s head of global pharma research, told reporters that the first products entering clinical trials from the alliance were likely to be tested in humans within two years. “We feel this is a very, very good investment,” Babiss said. “This should greatly complement our approaches of using small molecules and monoclonal antibodies and peptides.”