Southern blot analysis of RT-PCR products. RT-PCR and no RT controls were carried out on total RNA from K562 cells, T47D (hCTR positive) and 3T3 (hCTR negative) cells employing hCTR and actin specific oligos. PCR products were size fractionated on a 1 % agarose gel and Southern blotted. hCTR and actin specific 32P end labelled probes were hybridized to blot. These results are representative of 3 independent experiments all giving similar results.