Immunodetection of the transgene products. (A) Two protein species of similar abundance were observed in spleen and bone marrow of transgenic animals by Western blot, corresponding to the expected hybrid protein (33.8 kD) and to a shorter form (26.8 kD) whose translation started from an initiation codon present in the second exon of the L-PK gene. As a control, human Bcl-2 protein was detected in human follicular t(14:18) B-lymphoma cells at 26 kD. (B) A similar pattern was observed on analysis of transgenic erythroid cells isolated from 13-day old fetal livers. Both transgene products were selectively detected in the membranous fraction of these cells and were absent from the cytosolic fraction.