The major long-range objective of the proposed research is to elucidate the mechanisms operative in the modulation of RNA polymerase activities during various growth and developmental transitions, emphasizing studies on the regulation of RNA synthesis in rapidly proliferating tissues. Special emphasis will be placed on (1) the regulation of RNA polymerase I activity during the transition of tissue from a quiescent to a highly proliferative state where the synthesis of rRNA is dramatically enhanced; (2) the identification of regulatory elements which control or modify RNA polymerase activities during normal growth and deveopment, abnormal growth induced by auxin, and abnormal growth induced by viral infection; and (3) an analysis of the conditions required for faithful transcription of specific genes by RNA polymerase I and II in vitro. The ultimate goals are (1) to elucidate the causal relationship (if any) between the induction of ribosome synthesis and tissue growth or proliferation; and (2) to determine the mechanisms by which certain hormonal (auxin) and viral agents modify RNA synthesis. The methodology employed to reach these objectives will focus on the following techniques: (1) Immunoprecipitation of 32P and 35S RNA polymerases from partially purified cellular fractions with antibodies to the native enzymes and their largest subunits; (2) Isolation, fractionation, and hybridization of in vitro synthesized mercurated RNA; (3) two dimensional gel electrophoresis to study modifications of RNA polymerase subunits during growth transitions.