FIG. 4.
MESV proviral DNA is highly methylated in ES but not fibroblast cultures. Genomic DNA was digested with EcoRV alone or together with SmaI, XmaI (control), or SacII and size separated by gel electrophoresis. After transfer to a nylon membrane, the DNA was hybridized with a lacZ probe and subsequently with a Neor probe, as indicated. The schematic diagram shows the fragments expected if digestion with either SmaI or SacII is not blocked or is only partially blocked by methylation. The percentage of LacZ-positive colonies determined at the time of DNA isolation for each clone is shown. bp, base pairs.