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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.