Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305-5307, USA. dMaier@genome.stanford.edu|Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305-5307, USA. dMaier@genome.stanford.edu|Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305-5307, USA. dMaier@genome.stanford.edu|Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305-5307, USA. dMaier@genome.stanford.edu