Characterization and properties of heteromeric plant protein complexes that interact with tef cis-acting elements in both RNA polymerase II-dependentpromoters and rDNA spacer sequences

The tef box, a cis-acting element identified in promoters of several plant genes encoding components of the translation apparatus, is involved in the activation of gene expression in cycling cells. In vitro, this element medi ates the formation of two protein complexes called C1 and C2. A tef-like bo x is also found within the intergenic transcribed spacer of several plant r RNA genes. In radish this sequence has already been described as a protein- binding site putatively involved in the regulation of rDNA expression and i s sufficient for formation of C1 complexes. By using mutated tef boxes, we show that tef-dependent activation of transcription is correlated with form ation of both C1 and C2 complexes in a context-dependent manner. In transie nt expression experiments, the activation of a minimal promoter-GUS gene fu sion is associated with the formation of C2 complexes. In contrast, the abi lity to form C1 complexes appears to allow activation of reporter gene expr ession in root meristems of transgenic Arabidopsis. SDS-PAGE analysis of pu rified protein fractions containing either the C1 or the C2 activity indica tes a complex heteromeric structure for these potential regulators. Thus, t he tef box seems to be a central component of the regulation of gene transc ription in distinct and overlapping developmental programs, and could be in volved in co-regulation of transcription by RNA polymerases I and II.