作者单位:San Francisco State Univ, Dept Biol, 1600 Holloway Ave, San Francisco, CA 94132 USA[1]Childrens Hosp Oakland Res Inst, 5700 Martin Luther King Jr Way, Oakland, CA 94609 USA[2]Univ Calif Berkeley, Dept Mol & Cell Biol, 142 LSA 3200, Berkeley, CA 94720 USA[3]