Structure of chick chromosomal genes for calbindin and calretinin

The chick chromosomal gene for calbindin (the 28,000 Mr intestinal calcium-binding protein) was cloned, and all the exons and flanking regions were sequenced. The promoter region contains typical ATAAA and GGGCGG boxes, the latter being unusual in "non-housekeeping" genes. Three polyadenylation signals are found in the calbindin gene that correspond to the three known mRNAs. Transcription termination is not efficient because homology with consensus sequences found downstream from the polyadenylation signal is weak. There are ten introns, most of which do not fall at homologous positions, neither with respect to the sixfold repeating structure of the calbindin protein, nor with respect to previously sequenced genes for calmodulin and other calcium-binding proteins. The gene for the related protein calretinin was cloned and partially sequenced. The introns are in the same positions in the calretinin and calbindin genes. The introns have apparently been inserted during the divergence of the calcium-binding protein superfamily.