8.A.6 The Auxiliary Nutrient Transporter (ANT) Family

A single functionally characterized protein of 2958aas, YLR087c of Saccharomyces cerevisiae (CSF1p) appears to function as an auxiliary protein, stimulating nutrient uptake at low temperatures. The protein is required for growth and sugar fermentation only at low temperatures (i.e. 4°). A CSF1 disruptant mutant exhibited about 4x lower glucose and L-leucine uptake rates than the wild type parent, but at 30°, the two strains showed the same rates of uptake. These results suggest that CSF1p associates with unidentified plasma membrane transporters to stimulate their activities at low temperatures. The protein shows limited sequence similarity near its N-terminus (residues 21-704) to comparable N-terminal regions in (1) a protein of 2042aas from Drosophila melanogaster (gbAE003653) and (2) another protein of 4158aas from Caenorabditis elegans (gbAC024791). CSF1p might be a regulator of certain nutrient transporters.