The Saccharomyces cerevisiae JEN1 gene encoding the lactate transporter undergoes strong catabolic repression at both transcriptional and post-transcriptional levels. JEN1 mRNA decay is greatly accelerated upon the addition of a pulse of glucose, fructose or mannose to induced Cell Cultures. Mapping of the 5'UTRs and 3'UTRs of JEN1 transcripts revealed multiple transcription start-sites located at position -51, +391 or +972, depending on the Cell Culture conditions. The presence of the JEN1(+391) transcript correlated with rapid glucose-triggered mRNA degradation of the JEN1(-51) transcript, whereas when the small transcript started at position +972, the JEN1(-51) mRNA turnover rate was unaffected. Overexpressed JEN1(+391) transcript accelerated JEN1(-51) mRNA decay in all conditions tested but was not translated. We propose that the JEN1(+391) transcript may have a "sensor-like" function, regulating glucose-triggered degradation of JEN1(-51) protein-coding mRNA. (c) 2005 Elsevier Inc. All rights reserved.