FIG. 1.

Tissue specificity of transgene expression in MMTV/MT-Y250F transgenic mice. (A and C) Structures of the MMTV/MT-Y315/322F (A) and MMTV/MT-Y250F (C) transgenes. The Bluescript vector backbone is represented by a thin line on either side of the expression cassette, with the cross-hatched region corresponding to the MMTV LTR derived from plasmid pA9, the stippled portion corresponding to the MT-Y250F cDNA with phenylalanine substitutions at amino acids positions 315 and 322 or amino acid position 250, and the solid region corresponding to the transcriptional processing sequences derived from the SV40 early transcription unit. The transcription start site is indicated by the arrow. (B and D) RNA transcripts corresponding to the MMTV/MT-Y315/322F (B) and MMTV/MT-Y250F (D) transgenes in various organs of the MT-Y315/322F transgenic strain as assessed by RNase protection. Tissues were derived from a virgin tumor-bearing female, a virgin female, and a male. The antisense probe used in this RNase protection analysis (MTR) is complementary to a 203-nucleotide fragment corresponding to the amino terminus of PyV MT and is marked by MT-315/322F and an arrow. Also shown is an RNase protection analysis with identical RNA samples and an antisense probe directed against PGK, which protects a 124-nucleotide fragment indicated by PGK and an arrow. M.Gl., mammary gland.