The lens protein alpha A-crystallin of the blind mole rat, Spalax ehrenbergi: evolutionary change and functional constraints.

The complete structure of the single-copy alpha A-crystallin gene of the blind mole rat (Spalax ehrenbergi) has been determined in order to elucidate the evolutionary effects of the loss of vision on a lens-specific protein and its gene. The alpha A-crystallin gene appears to have all the necessary transcriptional and translational signal sequences to be expressed in the rudimentary lens of the mole rat and gives rise to probably two protein products by means of alternative splicing, as in rodents with normal vision. Comparisons of the blind mole rat alpha A-crystallin sequence with alpha A sequences from other rodents reveal a considerable acceleration of the substitution rate at nonsynonymous positions in the mole rate lineage, which reflects a relaxation of selective constraints, but the acceleration is not to the extent that might be expected if the gene were now without any function. The remaining evolutionary constraints still imposed upon the mole rat alpha A-crystallin gene may possibly reflect the need for alpha-crystallin expression as an indispensable component in the developmental program of the atrophied eye.