Chicken ornithine transcarbamylase gene, structure, regulation, and chromosomal assignment: repetitive sequence motif...

Ornithine transcarbamylase (OTC) is one of the urea cycle enzymes. While the chicken is a uricotelic animal, it has measurable OTC activity in its kidney. OTC activity is highly variable within and between chicken breeds. Chicken OTC may have some physiological significance because of its significant activity in the kidney. We cloned the OTC cDNA from chicken kidney and found 77% homology between the deduced amino acid sequence of the mature protein and that of mammals. The chicken OTC gene spans 26 kb, consists of 10 exons and 9 introns, and utilizes the same exon-intron boundaries as the human gene. The 5'-flanking region contains a putative TATA box and two potential regulatory sites, but neither the 5'-flanking region nor the splice sites correlated with variation in OTC activity. In intron 3, two polymorphic sites were found: one comprising a deletion of 401 nucleotides; and the other was a length and sequence polymorphic region located 8 bases upstream from the deletion. The latter polymorphism provides an explanation for phenotypic variation in OTC. Linkage analysis has suggested reassignment of the chicken OTC gene from the suggested Z chromosome to chromosome 1q.