A possible mechanism of transcriptional delay shown for the type II ATPase operon. A physical block (red ellipse), which might be built by proteins, congestion of polymerases or convergent polymerases, decelerates the polymerase velocity (0 minutes). After a certain time the block is disintegrated and stalled polymerases can continue with elongation of mRNA (10 minutes and 20 minutes), leading to a relative increase of mRNAs as a function of time and distance. TSS is the transcriptional start site of the operon. The insert on top shows gene expression over time of all genes of the ATPase operon starting with atp1 (dark blue line) and ending with PMM1447 (conserved hypothetical in light blue). For better visualization the operon was plotted in three separate graphs. The microarray signal intensity (expression) was normalized to time 0 h.