Search

The nucleotide sequence of the cDNA, containing coding region of the alpha-subunit of the pig kidney Na+, K+-ATPase, was determined. The region contains 3063 b.p. coding for 1021 amino acid residues. In the course of processing, five amino acid residues are cleaved to yield the mature Na+, K+-ATPase alpha-subunit containing 1016 amino acid residues.

Five different nucleotide sequences have been found in the human genome homologous to the gene of the alpha-subunit of Na+,K+-ATPase. A comparative analysis of the primary structure of these genes in the region 749-1328 (in coordinates of cDNA from the pig alpha-subunit) is presented.

Complete primary structures of both subunits of Na+,K+-ATPase from various sources have been established by a combination of the methods for molecular cloning and protein chemistry. The gene family homologous to the alpha-subunit cDNA of animal Na+,K+-ATPases has been found in the human genome. Some genes of this family encode the known isoforms (alpha I and alpha II) of the Na+,K+-ATPase catalytic subunit. The proteins coded by other genes can be either new isoforms of the Na+,K+-ATPase catalytic subunit or other ion-transporting ATPases. Expression of the genes of this family proceeds in a tissue-specific manner and changes during the postnatal development and neoplastic transformation. The complete exon-intron structure of one of the genes of this family has been established. This gene codes for the form of the catalytic subunit, the existence of which has been unknown. Apparently, all the genes of the discovered family have a similar intron-exon structure. There is certain correlation between the gene structure and the proposed domain arrangement of the alpha-subunit. The results obtained have become the basis for the experiments which prove the existence of the earlier unknown alpha III isoform of the Na+,K+-ATPase catalytic subunit and have made possible the study of its function.

The primary structure of the putative regulatory region of a gene of the Na+,K+-ATPase multigene family in the human genome has been determined. This region includes the first exon with all of the untranslatable sequence of mRNA and a dozen nucleotides, coding for the first four amino acids of the hypothetic precursor of the alpha+-subunit. The entire region comprises over 1400 bp. The possible role of specific nucleotide blocks within this region in comparison with other genes is discussed.

mRNA coding for beta-subunit of Na+, K+-ATPase from pig kidney is about 24-25S as deduced from the hybridization pattern of poly (A)+-RNA with two synthetic oligonucleotides structurally corresponding to two peptides isolated from the tryptic hydrolyzate of beta-subunit. Cloning of cDNA allowed to determine the complete structure of the gene and to deduce the amino acid sequence of beta-subunit of Na+, K+-ATPase. The beta-subunit contains 302 amino acid residues and the protein is not processed at the N-nor at the C-terminus.

Oligonucleotides deduced from the amino acid sequence of a hexapeptide Lys-Asp-Phe-Ala-Glu-Asn were synthesized and used as probes to screen a pig kidney cDNA library for a specific DNA sequence coding for the alpha-subunit of Na+, K+-ATPase. It was shown that the mixed oligoprobe, consisting of 64 heptadecamers, could be only suitable for mRNA blot analysis. To identify the clones with specific cDNA inserts, mixed oligoprobes were fractionated by HPLC technique. For the same purpose a new set of oligonucleotides, synthesized as four groups of 16 different heptadecamers each, was used.

The expression of genes coding for alpha and alpha III isoforms of Na+,K+-ATPase alpha-subunit has been studied in human kidney, brain, thyroid and liver cells. The expression was shown to be subjected to a tissue-specific control and also depended on the developmental stage. The tissue-specific expression of genes coding for different isoforms of the catalytic subunit of Na+,K+-ATPase perhaps may be attributed to various functions of proteins belonging to this family.