We have identified and characterized a 12th subfamily of vertebrate annexins by systematic analysis of the primary structure, chromosomal mapping, and molecular evolution of unique cDNA and protein sequences from human and mouse. Distinctive features included rare expression, a codon deletion in conserved repeat 3, and an unusual ablation of the type II calcium-binding sites in tetrad core repeats 1, 3, and 4. The paralogy of novel annexin A10 (following revised nomenclature) was confirmed by FISH- mapping human ANXA10 to chromosome 4q33 and genetic linkage mapping mouse Anxa10 to midchromosome 8. Phylogenetic analysis established that the 5' and 3' halves of the annexin A6 octad are more closely related to annexins A5 and A10, respectively, than they are to each other. Molecular date estimates, paralogy linkage maps between human chromosomes 4 and 5, and annexin structural considerations led to the proposal that annexins A5 and A10 may have been the direct progenitors of annexin A6 octad formation via chromosomal duplication during the genome expansion in early chordates.
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