RNA decay profiles of type I and type II operons. Both type I (left panel) and type II (right panel) operons have delayed decay profiles that are more pronounced with distance from the promoter. Type I operons are characterized by a plateau in transcript levels prior to decay whereas transcript levels in type II operons increase with time prior to decay and this increase is greater with distance from the promoter. The order of genes within each operon is indicated by numbers in parentheses. The microarray signal intensity (expression) was normalized to time 0 h.