Expression analysis of five human GBM cell lines by semiquantitative RT-PCR. Total RNA from the five GBM cell lines U87, U138, U251, U343 and GaMG was used for semiquantitative RT-PCR analysis. The primers for detection of the full length HERV-K mRNA, the deletion mutant, the spliced envelope (env) mRNA, the double spliced rec and the 1.5 kb mRNA are described in. Their localization within the HERV-K provirus is shown in Figure 1. The length of the cDNA amplicons in base pairs (bp) is shown on the right side of the figure. As positive control (+) cDNA of the teratoma cell line PA1 was used. The various cDNA concentrations were normalized to that of the housekeeping gene GAPDH. As a test for contamination with genomic DNA, which would interfere with full length HERV-K mRNA detection, a PCR reaction was performed using an aliquot of the mRNA before reverse transcription (Control).