Table 1. Sigma factors and transcription factors associated with genes exhibiting low or high levels of expression noise.

Transcription factor	Number of target genes	Noise level	p-value (two-sided Wilcox rank test)
MetJ	10	low	0.0016
σ32	64	low	0.0052
CpxR	18	low	0.011
ArgR	16	low	0.017
NarP	6	high	0.039
TrpR	6	high	0.029
GadX	10	high	0.027
Fnr	71	high	0.015
Hns	43	high	0.0099
GadW	5	high	0.0089
NarL	19	high	0.0086
IhfA/B	48	high	0.007
σ38	85	high	6.7e-7

We analyzed all factors listed in RegulonDB that regulate five or more targets (6 sigma factors and 43 transcription factors in total). All factors with p-values less than 0.05 (uncorrected for multiple tests) are shown.