The effect of removal of band-3 N-terminus and of protein-4.2 HS mutations on the enhancement of B3-specific chloride transport by protein 4.2. The cRNAs encoding either band 3 (B3) or band-3 membrane domain (BM) were injected into oocytes either alone or with protein 4.2 or protein-4.2 variants. DNDS-sensitive chloride influx (20 min) was measured 24 hours after injection with cRNA using groups of 12 to 15 oocytes as described previously.³⁰  Results are shown as means ± SEM for comparisons with the relevant B3 alone sample by Student t test: ^**P < .005, ^*P < .05. Similar results to those shown in panels A and B have been observed in at least 3 separate experiments. Panel A shows the effects of the removal of the B3 N-terminus (construct BM) on the 4.2 enhancement effect. B3 (0.5ng) or BM (0.3 ng) cRNAs were coinjected with 1 and 2 ng protein 4.2. Protein 4.2 only enhanced B3-specific chloride transport and not that of BM. This result is consistent with the protein-4.2 binding site being on the B3 N-terminus. Panel B shows the effect of 3 different HS mutations (4.2 Nippon, 4.2N; 4.2Tozeur, 4.2T; 4.2Komatsu, 4.2K) on the ability of protein 4.2 to enhance band-3 chloride transport. In panel B, 0.5 ng B3 cRNA was coinjected with 1.5 ng protein 4.2 or protein-4.2 variant cRNA. Protein 4.2 Nippon increased the chloride uptake induced by intact B3 nearly as much as normal protein 4.2. Neither protein 4.2 Tozeur nor protein 4.2 Komatsu had an effect on chloride uptake when coexpressed with intact B3.