Figure 5.

Expression pattern and chromatin modifications of classes I, II and III ERVs. Quantitative RT–PCR analysis of (A) eMLVs (class I), (B) IAP (class II) and (C) MERV-L (class III) messenger RNA expression in embryonic and differentiated cells. Bars represent the mean±s.e.m. of three independently prepared samples, relative to three control genes (UBC, CYCA and Gapdh). ChIP-based measurement of (D) H3K9me3 and (E) H3K27me3 at the viral sequence of cells infected with MLV containing neo^r with PBSpro or PBSproB2 and selected for 14 days or infected without selection. Relative enrichment values (% of input) in all ChIP experiments were normalized to the relative enrichment at the Gapdh promoter. Negative and positive control genes gave the expected enrichment (not shown). ChIP, chromatin immunoprecipitation; MLV, murine leukaemia virus; ERV, endogenous retrovirus; PBSpro, proline tRNA primer-binding site; RT–PCR, reverse transcription PCR.