Rat galactose-1-phosphate uridyltransferase coding sequence, transcription start site and genomic organization.

Galactosemia is an inborn error of metabolism in humans due to deficient activity of the enzyme galactose-1-phosphate uridyl-transferase (GALT). Using a 1.3 kb Bam HI restriction fragment of the human GALT cDNA as a probe, three cDNAs, 786 bp, 265 bp and 1.4 kb were isolated from a rat liver cDNA library. The total rat GALT coding sequence obtained from these three clones was 1051 nt. Repeat cDNA library screening failed to isolate cDNA clones with additional 5'-coding sequence. Using the 786 bp cDNA as a probe, three genomic clones, RGG1, RGG2, and RGG3 were isolated from a rat genomic library. RGG2 and RGG3 contained additional 5'-coding sequence, missing from the cDNA clones, which was identified by comparison with the human cDNA sequence. The rat GALT sequence, from transcription start site to the polyadenylation tail, is 1254 nt and is divided into 11 exons which span over 3.5 kb of genomic sequence. Primer extension identified the transcription start site as 17 nt 5' to the translation start site. Rat GALT is 379 amino acids long, identical to human GALT, with a derived molecular weight of 43,312 Da similar to the 43,360 Da weight for human GALT. The derived rat amino acid sequence is 90% identical to the human sequence. The isolation of rat GALT genomic sequence will facilitate future investigations of the regulation of expression of the rat GALT gene.