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    Gene. 1995 Apr 3;155(2):179-84.

    Characterization and quantification of full-length and truncated Na,K-ATPase alpha 1 and beta 1 RNA transcripts expressed in human retinal pigment epithelium.

    Ruiz A, Bhat SP, Bok D.

    Department of Anatomy and Cell Biology, School of Medicine, University of California, Los Angeles 90024, USA.

    We have characterized cDNA clones encoding the alpha 1 and beta 1 subunits of Na,K-ATPase produced in the human retinal pigment epithelium (hRPE). In addition to isolating clones corresponding to known sequences of Na,K-ATPase subunits, we report hitherto unknown forms of Na,K-ATPase with unique deduced amino acid (aa) sequences in their C-termini. Truncated cDNA sequences were found for both the beta 1 and alpha 1 subunits. While the beta 1 sequence is truncated by two aa residues at the C terminus, in the alpha 1 sequence 342 aa have been replaced by a unique sequence containing only 44 aa. Interestingly, this new C-terminal polypeptide shows sequence similarities to the Ca(2+)-ATPase and contains consensus sequence elements for phosphorylation and cell adhesion, suggesting expression of Na,K-ATPase subunits with unique functions. Using reverse transcription-polymerase chain reaction, RNA sequences for alpha 1, beta 1 and their corresponding truncated isoforms were quantified. 4.0 x 10(5) alpha 1 and 2.3 x 10(5) beta 1 molecules were found per ng of mRNA from hRPE. Much lower levels were detected for truncated alpha 1 and beta 1 (3.6 x 10(3) and 2.7 x 10(3) molecules/ng, respectively). These data corroborate the expression of truncated transcripts coding for unique aa sequences in hRPE, and suggest that factors other than alpha 1 and beta 1 mRNA levels regulate the equimolar accumulation of alpha and beta subunits in the plasma membrane.

    PMID: 7536695 [PubMed - indexed for MEDLINE]

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