Abstract
Present understanding of gene expression in erythropoietic tissues is derived solely from studies of the globin genes. Of the three distinct carbonic anhydrase (carbonate dehydratase; carbonate hydro-lyase, EC 4.2.1.1) isozymes, carbonic anhydrase I is erythrocyte-specific and, in humans, is under developmental control. The appearance of carbonic anhydrase I in the erythrocyte late in fetal life follows closely the gamma- to beta-globin switch. In order to study the expression of this erythrocyte-specific nonglobin protein, we set out to isolate a cloned carbonic anhydrase I cDNA. A mixture of 17-base-long synthetic oligonucleotides was used as an in situ hybridization probe to screen a rabbit reticulocyte cDNA library. Two clones were isolated, and the complete nucleotide sequence of the clone with the largest insert was determined and shown to code for carbonic anhydrase I. This clone, designated pRCAI, is near full length and has provided the 40% of the amino acid sequence of rabbit carbonic anhydrase I, which was not known hitherto. The deduced primary structure has revealed potentially significant changes in the vicinity of the active site of the rabbit carbonic anhydrase I when compared with carbonic anhydrase I and II sequences from other species.