Structure and expression of a cloned cDNA for human (2'-5')oligoadenylate synthetase.

17S poly(A)+RNA, which hybridized to an oligonucleotide complementary to a part of the partial cDNA (E1cDNA) (Merlin et al. (1983) Proc. Natl. Acad. Sci. U.S. 80, 4904) for 2-5A synthetase, was isolated from interferon-treated human KB cells and used for cDNA cloning. Several overlapping cDNAs were cloned by using the oligonucleotide as a probe. Two of them were joined at their overlapping region, resulting in a cDNA (22-1 cDNA) of 1.4 kb containing a long open reading frame. When the cDNA was expressed in COS-7 cells with an eukaryotic promoter, active 2-5A synthetase was produced and localized mainly in the cytoplasm. The 5'-proximal ATG in 22-1 cDNA is followed immediately by another ATG. This second ATG was assumed to work as the initiator codon. If so, this enzyme comprises 363 amino acids.