fig4

Figure 4. RNase protection analysis of upstream transcriptional start sites. A: total RNAs, extracted from K562 parental cells (ABCB1 mRNA negative control), KB-C1 cells (ABCB1 mRNA positive control), and three drug-resistant variants (K562/R7, RVC and RDC), were hybridized with the antisense RNA probe described below in Figure 4B. Primer extension products (lane 1) were used to map the locations of the transcription starting sites (-324-bp, and -130/-134-bp) upstream of the translation starting codon of the ABCB1 gene; B: structural presentation of the genomic probe (the 982-bp PstI-PstI genomic fragment) of the ABCB1 proximal promoter used for generating the antisense probe used in the RNase protection assays; C: the densitometric values (i.e., the mean density of the area/band of interest) are determined by using the ImageJ software. ABCB1 mRNA transcript levels, relative to R7 cells, were determined by calculating the ratios of the mean densitometric values between the cells of interest and R7 cells