Effects of mutant transcripts of GATA1 on the expression level of the truncated protein. The GATA1 mutations observed in TAM patients are classified according to the types of transcripts. The translational efficiency of each transcript was assessed by Western blot analysis in BHK-21 cells transfected with GATA1 cDNA expression vectors (top part of the panel) and Northern blot analysis (bottom part of the panel), respectively. WG indicates wild type GATA1; SP, splicing error mutation (Δexon 2); L, loss of first methionine mutation; P1, PTC type 1 mutation; P2, PTC type 2 mutation. The details of the GATA1 mutations are summarized in Table 1. NeoR indicates Neomycin phosphotransferase II.