Ia Genes, Gene Products, and Determinants
The I region of the mouse H-2 gene complex codes for four Ia genes, Aα, Aβ, Eβ and Eα, whose gene products express the Ia determinants. Aα, Aβ and Eβ map within the I-A subregion, while Eα maps to the I-E subregion. Aα and Eα genes code for a 34,000 dalton polypeptide while Aβ and Eβ genes code for a 28,000 dalton polypeptide. The noncovalent association of AβAα and EβEα form the I-A and I-E Ia molecules.
Recent studies have confirmed the order of the Aα, Aβ and Eα genes within the I-A subregion. Confirmational determinants Ia.22 and Ia.23 can be localized to the N-terminal of the Eβ polypeptide while Ia.50 is localized to the C-terminal of the Eβ chain. Studies using monoclonal antibodies have suggested that multiple Ia.2-like determinants may be located in different domains of the Aβ chain and similar Ia.7-like determinants may be located throughout the Eα chain. Recent studies have suggested that duplicated Aα, Aβ, Eβ and Eα genes may exist. Each of them would carry some common Ia determinants and some unique Ia determinants identified by monoclonal antibodies. Random association of the polypeptide chains could generate multiple Ia molecules, and numerous combinatorial determinants. This could account for the diversity seen with Ia antigens in antigen presentation.
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