MOLECULAR-CLONING OF MOUSE ERYTHROCYTE PROTEIN-4.2 - A MEMBRANE-PROTEIN WITH STRONG HOMOLOGY WITH THE TRANSGLUTAMINASE SUPERGENE FAMILY

We report the molecular cloning and characterization of mouse erythroc yte protein 4.2 (P4.2). Mouse erythrocyte P4.2 is a 691-amino-acid pro tein with a predicted MW of 77 kDa. Northern blot analysis detected a 2.2-kb transcript in mouse reticulocytes, compared with a 2.4- to 2.5- kb transcript in human reticulocytes, which is consistent with the abs ence of the 30-amino-acid splicing insert in mouse erythrocyte P4.2 th at is found in the human protein (isoform I). Like the human erythrocy te P4.2, mouse erythrocyte P4.2 contains regions strikingly homologous with the transglutaminase (TGase) proteins although it too most likel y lacks TGase crosslinking activity. Mouse P4.2 is on average 73% iden tical with human erythrocyte P4.2, although regional variations exist, with greatest conservation in the regions of the molecule that contai n the TGase active site, the TGase calcium-binding site, and a band 3 binding site. Hydropathy analysis reveals a protein containing a serie s of hydrophobic domains, similar to the situation for human P4.2 and consistent with its tight binding to the membrane, although the mouse P4.2 is missing both the strongly hydrophilic region and adjacent high ly charged region that are present in the human protein, suggesting th at the two proteins could differ in their physical characteristics, bi nding associations, or functional properties. The availability of the complete mouse erythrocyte P4.2 cDNA should help in the design of P4.2 -deficient animal models (for example, ribozyme or homologous recombin ant ''knockout'' models) that should accelerate the understanding of P 4.2 function in both erythroid and non-erythroid cells.