Expression pattern of the PK-bcl-2 transgene. Hybrid PK-bcl-2 transcripts were selectively detected in the liver and erythropoietic tissues (spleen and bone marrow) by Northern blot analysis. A total of 10 μg of total RNAs were electrophoresed on a formaldehyde agarose-gel. After transfer, the membrane was hybridized with a human bcl-2 probe. Normalization of total RNA amounts was made by hybridizing the membrane with an 18S ribosomal RNA-specific probe.