Functional analysis of the mouse galactose-1-phosphate uridyl transferase (GALT) promoter

Galactose-1-phosphate uridyltransferase (GALT) is expressed in most tissues , but the near total absence of catalytic activity in humans with the disea se galactosemia leads to specific organ, dysfunction, the pathophysiology o f which remains an enigma. To characterize the transcriptional regulation o f the mouse GALT gene, we isolated and sequenced over 3 kb of a 5'-flanking sequence and functionally characterized the region using in vitro transien t transfection and in transgenic mice. A minimal promoter of 145 bp was fou nd to function in both HepG2 cells and NS20Y mouse neuroblastoma cells. The minimal promoter contains regions of homology to the corresponding rat and human GALT genes. In transgenic mice expressing a luciferase transgene und er control of a 1.9-kb fragment of the mGALT promoter region, reporter acti vity was found in most tissues, with higher than expected reporter levels i n neonatal brain. To determine if high galactose levels in tissues could in duce promoter activity, we bred the mGALT:luciferase transgene into a line of mice in which the GALT gene function has been eliminated by homologous r ecombination. High tissue levels of galactose and metabolites did not induc e reporter activity above background. The studies show that GALT transcript ional regulation is complex and not directly induced by substrate levels. ( C) 2001 Academic Press.