A REASSESSMENT OF MAMMALIAN ALPHA-A-CRYSTALLIN SEQUENCES USING DNA-SEQUENCING - IMPLICATIONS FOR ANTHROPOID AFFINITIES OF TARSIER

alpha A-crystallin, a major structural protein in the ocular lenses of all vertebrates, has been a valuable tool for molecular phylogenetic studies. This paper presents the complete sequence for human alpha A-c rystallin derived from cDNA and genomic clones. The deduced amino acid sequence differs at two phylogenetically informative positions from t hat previously inferred from peptide composition. This led us to exami ne the same region of the alpha A-crystallin gene in 12 other mammalia n species using direct sequencing of PCR-amplified genomic DNA. New se quences were added to the database, and corrections were made to all a nthropoid sequences, defining clear synapomorphies for anthropoids as a clade distinct from prosimians. Within the anthropoids there are fur ther synapomorphies delineating hominoids, Old World monkeys, and New World monkeys. Significantly, sequence revisions and the addition of n ew sequence for a prosimian, the sifaka, eliminate the previous suppor t for the proposed anthropoid affinities of the tarsier inferred from alpha A-crystallin protein sequences. In addition, DNA sequences provi de greater resolution of certain relationships. For example, although they are identical in protein sequence, comparison of DNA sequences cl early separates mouse and the common tree shrew, grouping the tree shr ew closer to prosimians. These results show that adding DNA sequences to the to the existing alpha A-crystallin database can enhance its val ue in resolving phylogenetic relationships.