2',5'-oligoadenylate synthetase gene in chicken: gene structure, distribution of alleles and their expression.

We have cloned the gene for chicken 2',5'-oligoadenylate synthetase (ChOAS) by the method of polymerase chain reaction with use of ChOAS cDNA sequence. The ChOAS gene is composed of five introns and six exons containing all of the sequence of the ChOAS cDNA from the start to the stop codon. The first five exons of ChOAS gene which encode the OAS catalytic domain have a similar structure to HuOAS1 gene including the exon-intron boundaries. However, the length of introns of ChOAS gene is only 1/7 of those of HuOAS1 gene. The sixth exon of the ChOAS gene encodes the ubiquitin-like (UbL) domain of two consecutive sequence (UbL1 and UbL2) homologous to ubiquitin. ChOAS encoded in a single copy gene has at least two alleles, OAS(*)A and OAS(*)B. The differences between these two alleles are in the sixth exon of the gene; a 96-nucleotide sequence in the UbL1 portion of OAS(*)A is deleted from OAS(*)B. No OAS(*)B gene was detected in nine lines of chickens tested other than Leghorns. Almost the same levels of ChOAS-A and -B proteins induced physiologically in erythrocytes were detected in infant chickens (2-week-old), but in grown-up chickens (6-month-old) the level of erythrocyte OAS-B was markedly reduced in most of B/B chickens. Thus, the UbL domain of ChOAS is responsible for the maintenance of the OAS level in the tissue.