Fig. 2. Cdc18 promotes origin firing in G₂ cells. (A) Schematic of replication intermediates detectable by 2D gel electrophoresis. The bubble arc corresponds to origin firing, the fork arc corresponds to passive replication, and the X-spike corresponds to recombination intermediates or termination events. (B) 2D gel of genomic DNA extracted from exponentially growing wild-type cells and probed with a 3 kb HindIII–KpnI fragment that recognizes the origin ars3001. (C) 2D gel of genomic DNA extracted from cdc25-22 cells and cdc25-22 nmt1-cdc18+ cells, probed for ars3001. Samples were collected at the indicated times (hours) following the shift to 37°C in the absence of thiamine.