Expression of MDR-1 and novel 252 bp in cell lines and normal tissues. (A) Northern analysis analyzing expression ofMDR-1 in parental Burkitt cells (EW 36) and two mulridrug resistant sublines (VCR.25 and VCR60). (B) Oligonucleotide hybridization of EW 36 and two resistant sublines (VCR.25 and VCR60). DNA blot shows the presence of two alleles in parental EW 36 cells. Amplification of the G allele occurs with vincristine selection. EW 36 cells do not express MDR-1 but selection in vincristine induces expression of the G allele. (C) RNase protection using a 319-bp hybridMDR-1 probe described in panel E. EW 36 and VCR60 cells protect a 252-bp band representing the non–MDR-1 sequences. In addition, VCR60 cells protect the full-length hybrid probe composed of non–MDR-1 and MDR-1 sequences. (D) PCR examining the expression in normal tissues and unselected cell lines, of the novel 252-bp sequences and a hybrid composed of the 3′ 162.bp of the novel sequence and 67 bp of MDR-1. The primers used for PCR are underlined in panel E. The novel 252 bp are constitutively expressed in all cells. In contrast, a hybrid MDR-1 product is detected only in the vincristine selected EW 36 cells. (E) Sequence of hybrid probe used in panel C. The 252 bp of novel non–MDR-1 sequence are represented in upper case, whereas the MDR-1 sequences are shown in lower case.