Credit:
National Institutes of Health (NIH) [GM085328 to N.B.L. and C.L.Z., GM055898 to N.B.L., GM067317 and GM085337 to R.R.G.]; Microsoft Research [UTA08-351 to R.R.G.]. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. Funding for open access charge: NIH [GM085328 to N.B.L. and C.L.Z.].