Three clusters of transcripts.
Three clusters of transcripts were identified through k-means clustering (Fig 6) and labelled I, II and III. Of these, II was the cluster of housekeeping transcripts. The average BoE of this cluster was 0.84, that is 7.6 fold higher than the value of 0.11 obtained for the remaining transcripts (Wilcoxon text, P-value < 2e-16). Transcripts in cluster II had also greater average size of promoter architecture: 16 versus 5 for others (Wilcoxon text, P-value < 2e-16).