Genomic configuration, MTS1 product expression and Rb phosphorylation in three cases with a short interstitial deletion. (A) Schematic representation of the 36-kb interstitial deletion occurring in the MTS locus in T39p, T117, and T127. Small vertical arrows indicate breakpoints. Large horizontal arrows indicate the transcriptional orientation. The DNA sequences involved in transcriptional activation of the promotor located 5′ to theMTS1 exon 1α in cells with physical or functional Rb inactivation24 are shown: I—-I. R: EcoRI; M:Mbo I, X: Xba I restriction sites. The Xba I site has been deleted by the V(D)J process in the T39p sample.7 (B) RT-PCR detection of ABL (30 PCR cycles) andMTS1α (26 PCR cycles) transcripts in T39p, T117, and T127 samples and in dilutions of Hela and PBMC RNAs into RS4;11 RNAs (results observed in this experiment for other T-ALL cases are shown in Fig 3A). PCR products were electrophoresed on agarose gels, transferred to filters and hybridized with specific radiolabeled oligoprobes. The Hela cell line expresses high level MTS1α; MTS1 is deleted on both alleles in the RS4;11 cell line. (C) Western blot analysis of p16^INK4a and actin proteins in T39p, T117, T127, and in a dilution of Hela cells in PBS. (D) Western blot analysis of Rb expression in T39P, T117, and T127 samples and in the K562 and SAOS2 cell lines. The K562 cell line expresses phosphorylated Rb proteins (Rb-P). Rb is deleted in the SAOS2 cell line. Dilutions of K562 cells into PBS have been studied. Rb: unphosphorylated Rb protein.