2 ELLIPTOCYTOGENIC ALPHA-I/74 VARIANTS OF THE SPECTRIN ALPHA-I DOMAIN SPECTRIN CULOZ (GGT-]GTT ALPHA-I-40 GLY-]VAL) AND SPECTRIN LYON (CTT-]TTT ALPHA-I-43 LEU-]PHE)

Spectrin α(I/74) elliptocytosis results from abnormalities involving the 'head' region of spectrin dimer. Increased susceptibility to trypsin enhances cleavage of the α spectrin chain, yielding an increased amount of the αI 74-kD fragment at the expense of the αI 80-kD parent fragment. Recently we showed that the mutations causing the Spα(I/74) abnormality may lie in the α- or the β-chain, and that spectrin Culoz and spectrin Lyon were two (α(I/74))α-variants, respectively. We now show that the spectrin Culoz αI domain undergoes prominent tryptic cleavage after Lys 42, whereas cleavage prevails after Arg 39 in spectrin Lyon. Applying the polymerase chain reaction (PCR) technique to exon 2 of the spectrin αI domain, we have established that the mutation responsible for spectrin Culoz is αI 40 Gly → Val; GGT → GTT. Applying the PCR technique to the cDNA derived from reticulocyte mRNA, we have shown that the mutation responsible for spectrin Lyon is αI 43 Leu → Phe; CTT → TTT. Studies of normal controls and of family members using dot blot hybridization with allele-specific oligonucleotide probes confirmed these results. Variants such as spectrin Culoz and spectrin Lyon should provide insight into a region that participates in spectrin dimer self-association and whose susceptibility to proteolysis must reflect subtle conformational changes.