We have found that the ectopic expression of a specific gene's 3′ untranslated region leads to the dose dependent loss, relative to gene copy number, of that specific mRNA and protein, as well as an associated protein, in a eukaryotic cell line. The loss of these proteins from the eukaryotic cell line also results in specific phenotypic changes in these cells, suggesting that we have created a dominant negative mutant. This gene's 3′ untranslated region is known to contain numerous AU sequences, reminiscent of other eukaryotic genes whose expression may be regulated by these sequences. The apparent control of gene expression by a truncated 3′ untranslated region sequence provides further evidence supporting the regulatory function of these regions. The resulting decrease in steady-state mRNA levels by the overexpression of a portion of that gene's 3′ untranslated region further suggests the possible existence of a factor(s) that may bind to this region, and thus regulate gene function via its mRNA. The use of a gene's 3′ untranslated sequence to create a specific dominant negative mutation may also be applicable to other eukaryotic genes whose expression is controlled by similar regulatory sequences.