AtUCP2: a novel isoform of the mitochondrial uncoupling protein of Arabidopsis thaliana

Mitochondrial uncoupling proteins (UCPs) play a central role in adaptive th ermogenesis in mammals. The UCPs dissipate the proton gradient formed throu gh respiration without ATP synthesis, and the freed energy is readily conve rted to heat, helping the animals to maintain their body temperature in col d environments. Recently, it was found that UCPs also function in plant mit ochondria. Subsequently, a cDNA clone encoding a UCP in potato was isolated . Whereas the UCP gene constitutes a multigene family in mammals, only a si ngle cDNA sequence has been reported so far for the potato UCP. Moreover, i t has been recently suggested that Arabidopsis has only a single nuclear ge ne for UCP. Here we report the existence of another UCP gene in the Arabido psis genome, showing for the first time the occurrence of a multigene famil y for the protein in higher plants. A cDNA analysis of this gene showed tha t the novel isoform possesses all typical features reported for known UCPs. However, the new gene, unlike the other gene in Arabidopsis and the gene i n potato, did not appear to respond to low temperature.