Southern blot analysis on gel purified K562 RT-PCR products. (A) RT-PCR products on total RNA from K562 cells employing hCTR specific primers were size fractionated on a 2% agarose gel. Two bands, corresponding in size to hCTR1a and hCTR1b, were individually purified and re-run on a 2% agarose gel followed by Southern blot analysis. The blot was hybridized with a 32P end-labelled probe common to hCTR1a and hCTR1b. (B) Blot in Fig. 2A was stripped of probe and re-hybridized with a 32P end-labelled probe corresponding to 16 amino acid insert in hCTR1b isoform. These results are representative of 2 independent experiments giving similar results.