Fig. 3.

Effect of phosphorylation of SIG1 on association with the RNA polymerase core enzyme in vivo. (A) Leaf extracts of wild-type plants harvested in the daytime were subjected to sucrose density-gradient centrifugation, followed by immunoblotting with anti-SIG1. Molecular masses are based on those of the native proteins in each fraction, as further analyzed by nondenaturing PAGE (4–12%, wt/vol, polyacrylamide gradient). (B and C) SIG1 transgenics (3-wk-old) were incubated with [³²P]orthophosphate in light at 75 μmol·m⁻²·s⁻¹ (B) or in the dark (C). The extracted proteins were fractionated by sucrose density-gradient centrifugation, and each fraction was then immunoprecipitated with anti-SIG1, run on SDS/PAGE, and autoradiographed.