The biochemistry of interferon

In humans, at least 24 related genes or pseudo-genes exist that code for the production of at least 16 distinct mature IFN-as. These can be assigned to one of two families, i.e. type I and II. Humans are capable of synthesizing at least 15 type I IFN-as and a single type II IFN-a. 

Individual IFN-as generally exhibit in excess of 70 per cent amino acid homology with each other. They are rich in leucine and glutamic acid, and display conserved cysteines (usually at positions 1, 29, 99 and 139). These generally form two disulfide bonds in the mature molecule. Their tertiary structures are similar, containing several a helical segments, but appear devoid of P sheets. 

Individual members of the IFN-a family each have an identifying name. In most cases the names were assigned by placing a letter after the a (i.e. IFN-aA, IFN-aB, etc.). However, some exceptions 

Gel-filtration analysis reveals bands of molecular mass 40-70 kDa. These represent dimers (and some multimers) of the IFN-y polypeptide. Its biologically active form appears to be a homodimer in which the two subunits are associated in an antiparallel manner. 

All IFN-stimulated genes are characterized by the upstream presence of an interferon-stimulated response element (ISRE). Signal transduction culminates in the binding of specific regulatory factors to the ISRE, which stimulates RNA polymerase Il-mediated transcription of 

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