Fig 1.

Detection of S and AS RNAs of the U3 ERV-9 LTR (1-2-3-4)₁ repeat region by directional RT-PCR. (a) PCR primers used to detect the 200-bp S and AS transcripts from the U3 ERV-9 LTR. (b) Directional RT-PCR analysis of ERV-9 LTR U3 RNAs in nonmalignant primary human cells and in human cancer cell lines. P (positive control) is the U3 ERV-9 LTR directly amplified from K562 genomic DNA, and N (negative control) is the U3 ERV-9 LTR directly amplified from K562 RNA treated with DNase I. ERV-9 LTR U3 products could not be detected in DNase I-treated RNA samples in any cell line (see Fig. S1a in the supplemental material). (c) Real-time PCR analysis of U3 AS and S RNAs in nonmalignant and cancer cell lines. U3 AS RNA was expressed at a significantly higher level than U3 S RNA in normal cells (P < 0.05) but not in cancer cells (P > 0.05). The relative ratio of U3 RNAs between two samples was measured with GAPDH as a cDNA loading control, but the absolute copy numbers of U3 RNAs were not assessed. Relative fold was calculated by setting AS RNA expression level in each cell line as 1-fold. t test was used to evaluate significance.