Cre-mediated activation and expression of the oncogenic K-ras allele. (A) PCR for 285-bp wild-type (WT) and 315-bp activated (Δ) K-ras alleles demonstrate presence of the activated allele in KPM+ and KM+ tissues. PCR demonstrates presence of PML-RARα transgene in KPM+ and KP+ tissues. B indicates bone marrow; L, liver; S, spleen. (B) Oncogenic K-ras expression in diseased KPM+ and KM+ spleens. Pan-ras antibody immunoprecipitates of spleen cell lysates were immunoblotted with antibodies specific for 21-kDa wild-type ras (α-ras G12) and oncogenic ras G12D (α-ras D12) proteins. WB indicates Western blot; IP, immunoprecipitation.