The MRI26194 and MRI53426 phenotypes are due to mutations in Sptb. (A) Mating between Sptb^MRI26194/+ by Sptb^MRI26194/+ mice occasionally produced homozygous pups displaying jaundice. (B) Giemsa-stained blood smears from WT and homozygous pups. (C) Schematic of the β spectrin protein indicating different structural domains, and the locations and predicted effects of the mutations identified in the MRI26194 and MRI53426 lines. (D) Western blot of whole RBC lysates from homozygous and WT pups separated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) on a 4% to 20% gel and probed using an antibody against the N-terminal of β spectrin, with actin and ankyrin-1 as loading controls. The expected size of the truncated β spectrin (24 kD) is indicated with an arrow. (E) Representative image of a Coomasie-stained SDS-PAGE gel containing erythrocyte membrane preparations from mutant and WT mice. (F) Images of western blots of major skeletal proteins in erythrocyte membrane preparations from mutant and WT mice. (G) Quantification of protein bands detected by western blot (3 mice per group).