The MHC class II-associated chicken invariant chain shares functional properties with its mammalian homologs

The nucleotide sequence of chicken invariant chain (Ii) was determined, and the amino acid sequence similarity with human Ii is 61%. Certain regions i mportant for the biological function of human Ii are highly conserved betwe en chicken and mammals. The cytoplasmic tail of chicken Ii fused to the pla sma membrane reporter molecule neuraminidase relocated the protein to endos omes. Moreover, like the mammalian orthologs, the cytoplasmic tail was foun d to contain two independent leucine-based endosomal sorting signals. Chick en Ii was found to interact with human Ii and crosslinking studies also ind icate that chicken Ii assembles as a trimer. The chicken Ii can furthermore bind the human MHC class II (HLA-DR1). Many of the functional properties b etween the chicken Ii and its mammalian orthologs are thus maintained in sp ite of their sequence differences. (C) 2000 Academic Press.