Aci-Reductone dioxygenases are key enzymes in the methionine salvage pathway. The mechanisms by which the expression of this important class of enzymes is regulated are poorly understood. Here we show that the expression of the mRNA encoding the yeast aci-reductone dioxygenase ADI1 is controlled post-transcriptionally by RNase III cleavage. Cleavage occurs in a large bipartite stem-loop structure present in the open-reading frame region of the ADI1 mRNA. The ADI1 mRNA is found upregulated in the absence of the yeast ortholog of RNase III Rnt1p or of the 5’‡3’ exonucleases Xrn1p and Rat1p. 3’-extended forms of this mRNA, including a polycistronic mRNA ADI1-YMR010W mRNA also accumulate in cells lacking Rnt1p, Xrn1p and Rat1p, or the nuclear exosome component Rrp6p, suggesting that these 3’-extended forms are subject to nuclear surveillance. Finally we show that the ADI1 mRNA is upregulated in heat-shock conditions in a Rnt1p-independent manner. We propose that Rnt1p cleavage targets degradation of the ADI1 mRNA to prevent its expression prior to heat-shock conditions, and that RNA surveillance by multiple ribonucleases helps prevent accumulation of aberrant 3’-extended forms of this mRNA that arise from intrinsically inefficient 3’-processing signals.