Characterization and properties of heteromeric plant protein complexes that interact with tef cis-acting elements in both RNA polymerase II-dependent promoters 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 mediates the formation of two protein complexes called C1 and C2. A tef-like box is also found within the intergenic transcribed spacer of several plant rRNA genes. In radish this sequence has already been described as a protein-binding site putatively involved in the regulation of rDNA expression and is sufficient for formation of C1 complexes. By using mutated tef boxes, we show that tef-dependent activation of transcription is correlated with formation of both C1 and C2 complexes in a context-dependent manner. In transient expression experiments, the activation of a minimal promoter-GUS gene fusion is associated with the formation of C2 complexes. In contrast, the ability to form C1 complexes appears to allow activation of reporter gene expression in root meristems of transgenic Arabidopsis. SDS-PAGE analysis of purified protein fractions containing either the C1 or the C2 activity indicates a complex heteromeric structure for these potential regulators. Thus, the tef box seems to be a central component of the regulation of gene transcription in distinct and overlapping developmental programs, and could be involved in co-regulation of transcription by RNA polymerases I and II.