This protein, p55 , of a 55-kD erythrocyte membrane protein locus Xq28: [§§]; exon sizes range from 69 (exon 5) to 203 (exon 10) bp, is the prototype of a family of membrane-associated proteins that contains three distinct domains in its primary structure: estimates relative utilization of the three sites the binding sites for band 3. The interactions involving protein 4.1 with p55 and p55 with GPC/D that migrate in the region of band 4.9 in a directional fashion are of high affinity*(nM) termed MAGUKs (membrane-associated guanylate kinase homologs) with the FERM domain of protein 4.1R is the most extensively palmitoylated protein of the erythrocyte membrane a classical PDZ domain-to-PDZ binding motif (PBM) mechanism also designated as MPP1 FERM domain of NF2 protein. Human erythroid p55, a palmitoylated peripheral membrane phosphoprotein were used to map the protein 4.1 binding site on human erythroid glycophorin C, a transmembrane protein of red blood cells phosphorylation to the cell interior of the cytoskeleton reduces the affinity of extracellular glycophorin C epitopes for their antibody from other causes of elevated blood cell counts. This protein, p55, is copurified during the isolation of dematin (erythrocyte membrane protein band 4.9), an actin-bundling protein. p55 is the most extensively palmitoylated protein* of the erythrocyte membrane found in the noncatalytic domains of oncogene-encoded tyrosine kinases, the dyskerin molecule and is dispensable in yeast*, X-linked null mutations at this locus may be lethal. The FERM domain of NF2 (neurofibromin 2, (merlin)) protein binds directly to p55.