Alternative splicing gives rise to two novel long isoforms of Zn-alpha 2-glycoprotein, a member of the immunoglobulin superfamily.

We have isolated, from a rat liver cDNA library, two cDNAs encoding novel long isoforms of Zn-alpha2-glycoprotein (Zn-alpha2-gp), a member of the immunoglobulin superfamily with a high degree of sequence similarity to class-I major histocompatibility complex (MHC) antigens. Nucleotide (nt) sequence analysis of these two novel cDNAs has revealed that they contain insertions of 138 and 123 nt between the second and third exons of Zn-alpha2-gp, resulting in in-frame insertions of 46 and 41 amino acids (aa), respectively. Analysis of the mechanism of generation of both isoforms, named Zn-alpha2-gpA and Zn-alpha2-gpB, has shown that they result from a series of alternative splicing events, including alternative use of two additional exons, and of two different 3'-splice sites present in the first of these novel exons. The occurrence of these alternative splicing events in Zn-alpha2-gp could contribute to increasing the diversity of this nonpolymorphic and soluble class-I MHC antigen.