Fig. 1. Activity of the ars3001 origin at restrictive temperature in the orp1-4 mutant. The orp1-4 cells were grown exponentially in EMM medium at 25°C before shift to 36°C. Samples were removed at the times indicated (in hours) at restrictive temperature, and the DNA was purified and subjected to 2D gel electrophoresis, blotted to a membrane and probed with radioactively labelled ars3001 DNA. In the top panel, the strong arc (the Y-arc) reflects passive replication of the region and the weaker arc above reflects the usage of the region as an origin of DNA replication.