Second RNAi pathway emerges

The publication of a study in Nature this week (August 15)—combined with a similar study in Science earlier this month (August 5)—could force a reexamination of how RNA interference (RNAi) works, said several in the field not involved in the studies. While RNA had been known to silence genes post-transcriptionally, researchers found that it does so in a different way, found previously in plants, at the transcriptional level in human cells.

"This is a strong, strong suppressive pathway," said the lead author of the Science paper, Kevin Morris, of the University of California, San Diego. Morris' team found that SiRNAs targeting the promoter of a green fluorescent protein gene transfected into human fibroblasts reduced its mRNA levels by about 70%.

Separately, University of Tokyo researchers report in Nature that exploiting the same basic pathway in mammary cells, they sliced two endogenous genes' mRNA levels by more than 80%. One gene...