Protein 4.2 (P4.2) comprises -5% of the protein mass of human erythrocyte (RBC) membranes. Anemia occurs in patients with RBCs deficient in P4.2, suggesting a role for this protein in maintaining RBC stability and integrity. We now report the molecular cloning and characterization of human RBC P4.2 cDNAs. By immunoscreening a human reticulocyte cDNA library and by using the polymerase chain reaction, two cDNA sequences of 2.4 and 2.5 kilobases (kb) were obtained. These cDNAs differ only by a 90-base-pair insert in the longer isoform located three codons downstream from the putative initiation site. The 2.4-and 2.5-kb cDNAs predict proteins of -77 and =80 kDa, respectively, and the authenticity was confimed by sequence identity with 46 amino acids of three cyanogen bromide-cleaved peptides of P4. Subcloning and Sequence Analysis. cDNA inserts from positive phage clones were subcloned into pBS(+) plasmids (Stratagene). Unidirectional deletion clones were generated by using BAL-31 exonuclease (13), and cDNA fragments were sequenced with T3 and T7 primers by the dideoxynucleotide chain-termination method (14). Sequence analysis and GenBank data base searches were performed by IBI Pustell sequence analysis software (International Biotechnologies). 5'-End Extension of cDNA. Three oligonucleotides were prepared in a technique based on the polymerase chain reaction (PCR) to synthesize the missing 5' sequence of the partial cDNA clone: pl was composed of nucleotides (nt) 7-23 of clone 7 (c.7); p2 was complementary to nt 36-52 of c.7 plus an EcoRI restriction site at its 5' end; p3 was composed of the EcoRI polylinker and the poly(dC) originally used for the first-strand cDNA synthesis when the library was constructed. The sequences of pl, p2, and p3 were, respectively, 5'-dTGAGGATGCTGTGTTCC-3', 5'-dTCGAAlJCGTACTC-CATGCGCTGAG-3', and 5'-dGCGGLAAlTCCCCCCCCCC-CCCC-3', with the EcoRI sites underlined. p2 and p3 were used as PCR primers, and the reticulocyte cDNA library (5 ,u with 106 phages per pl) was used as a template. The reaction product was electrophoresed and stained with ethidium bromide. The major band was excised and subcloned into pGEM 3zf plasmids (Promega). From >500 transformants, 24 colonies were randomly chosen to make minipreparations of plasmid DNA, of which 80%o were positive when hybridized with 32P-labeled pl. tTo whom reprint requests should be addressed. IThe sequences reported in this paper have been deposited in the GenBank data base (accession nos. M30646 and M30647).
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