In humans, the OAS gene family consists of four genes:
- OAS1
- OAS2
- OAS3 and the
- OAS like protein - OASL.
OASL does not possess 2'5' OAS activity (Rebouillat D et al. 1999). The OAS1, OAS2 and OAS3 genes are encoded by a tightly coupled locus on 12q24.1. The additional member of the human OAS family is the OASL gene, which is localized to 12q24.2. Alternative splicing increases the number of distinct isoforms to 11:
- OAS1 encodes five isoforms at oligoadenylate synthetases (p42, p44, p46, p48 and p52).
- OAS2 encodes 2 OAS isoforms (p69 and p71)
- OAS3 mRNA is spliced in only one way and leads to the expression of the protein p100
- OASL encodes three OAS isoforms (p30, p45 and p59) (Rebouillat D et al. 1998)
Each OAS gene consists of a conserved OAS unit composed of five translated exons (exons A-E). Synthesis of the various oligoadenylate synthetases is induced in response to viral infection by type I IFN via IRF1 (Behera AK et al 2002). Gene activation occurs through the binding of dsRNA (142) or hairpin structures such as HIV-1 TAR RNA. This leads to oligomerization of the OAS or formation of 2-5 A dimers (OAS3) (170). This now active OAS is capable of polymerizing ATP. The result is 2-5 A oligomers (OAS1 and OAS2) or 2-5 A dimers (OAS3) (Rebouillat D et al. 1999).