In an effort to identify novel regulatory plant genes, conditional overexpression of toxic Arabidopsis thaliana gene products in Saccharomyces cerevisiae was evaluated as a genetic selection scheme. The screening method was tested on a fraction of a cDNA expression library and led to the identification of two Arabidopsis cDNA clones that were toxic to yeast; one corresponded to histone H1 and the other to a previously unidentified gene. This new gene, named ATL2, combines a RING-like zinc-binding motif and a putative signal anchor sequence for membrane insertion in the same molecule. Furthermore, inspection of the 3' untranslated region reveals two types of sequences which appear to be key determinants in rapid transcript decay. Indeed, rapid and transient accumulation of transcript occurs in the presence of a protein synthesis inhibitor and of the growth regulator auxin. These features provide evidence that ATL2 is an early-response gene. Thus, ATL2 represents one of the first early-response plant genes to be described which possesses a distinct regulatory domain; the fact that ATL2 mRNA is induced by auxin suggests that it might have a role during the response of plants to this growth regulator.