FIG. 1.

Induction of aggregative and postaggregative gene expression. RI9, ^act15cAR1, ^act15cAR2, and ^act15cAR3 cells were incubated in DB in the absence of stimuli, with either 30 or 600 nM cAMP pulses delivered at 6-min intervals, or with 300 μM cAMP delivered at 60-min intervals. Cells were then incubated for an additional 8 h with 300 μM cAMP/h. Samples were taken for RNA extraction at 0, 2, 4, 6, 12, and 14 h of incubation. Northern blots were hybridized to ³²P-labeled DNA probes for the aggregative gene csA, the postaggregative genes RasD and CP2, and the prespore genes psA and CotC. The experiment was repeated twice with similar results.