A MULTIPLE-STIMULI-RESPONSIVE AS-1-RELATED ELEMENT OF PARA GENE CONFERS RESPONSIVENESS TO CADMIUM BUT NOT TO COPPER

The expression of parA, an auxin-regulated gene expressed during the c ulture of tobacco (Nicotiana tabacum L.) mesophyll protoplasts, is ind uced by cadmium. To identify the cadmium-responsive element, we examin ed the parA promoter using the GUS reporter gene. Cadmium responsivene ss was retained in a 5' deletion of the parA promoter to -78 bp, but i t was nullified by further deletion to -49 bp, which implies that the region -49 to -78 bp contained a cadmium-responsive element. This regi on contains a sequence similar to as-1, an enhancer sequence from the cauliflower mosaic virus 35S RNA promoter that binds the nuclear facto r ASF-1. We named the sequence in the parA promoter pas. Gel-shift ass ays revealed that pas and as-1 compete for the same DNA-binding nuclea r protein(s). Since pentamers of either pas and as-1 were able to conf er cadmium responsiveness on a minimal promoter but mutant as-1 was no t, we propose that pas and as-1 are involved in cadmium-responsive gen e expression. Neither pas nor as-1 conferred responsiveness to copper. The specificity of this response, involving the function of as-1-rela ted elements including pas, is discussed.