THE TEF1 BOX, A UBIQUITOUS CIS-ACTING ELEMENT INVOLVED IN THE ACTIVATION OF PLANT GENES THAT ARE HIGHLY EXPRESSED IN CYCLING CELLS

In Arabidopsis thaliana, the tef1 box is a cis-acting promoter element of the EF-1 alpha A1 gene involved in the activation of transcription in meristematic tissues. The initiation of root calli in transgenic A rabidopsis by 2,4-D shows that the tef1-dependent expression of the GU S reporter gene is not restricted to meristematic regions but involves all of the cycling cells. Hybridization experiments conducted using A rabidopsis cDNA clones organized in a dense array on filters, and cDNA probes prepared from cells in various states of growth, or blocked at different steps of the cell cycle, indicate that the enhanced express ion of EF-1 alpha genes occurs in cycling cells at the point of entry into the cell cycle and remains constant during transit through the cy cle. The analysis of several promoters of genes, other than EF-1 alpha , which are overexpressed in growing cells and involved in the process es of translation or redox regulation, reveals the presence of sequenc es showing partial homologies with the tef1 box. The Arabidopsis ribos omal gene srp18 and the tobacco gene thioh2, encoding a thioredoxin h, contain such sequences. Gel retardation experiments suggest that thes e sequences are targets for the same proteins as those that interact w ith the tef1 box of the Arabidopsis EF-1 alpha A1 gene. In transfected Arabidopsis protoplasts, the putative tef1 sequence thioh2 partially restores the activity of a tef1 box-less EF-1 alpha A1 promoter. These data demonstrate that the tef1 box is a ubiquitous cis-acting element involved in the transcriptional activation of plant genes that are ov erexpressed in cycling cells. The deduced consensus sequence of the te f1 box is arGGRYAnnnnnGTaa. The key role that this regulatory element may play in the cell cycle, by pleiotropic control of the expression o f genes encoding components of the translational apparatus or involved in regulating the redox state of the cell is discussed.