High constitutive activity of a broad panel of housekeeping and tissue-specific cis-regulatory elements depends on a subset of ETS proteins

Enhancers and promoters that control the transcriptional output of terminally differentiated cells include cell typespecific and broadly active housekeeping elements. Whether the high constitutive activity of these two groups of cisregulatory elements relies on entirely distinct or instead also on shared regulators is unknown. By dissecting the cisregulatory repertoire of macrophages, we found that the ELF subfamily of ETS proteins selectively bound within 60 base pairs (bp) from the transcription start sites of highly active housekeeping genes. ELFs also bound constitutively active, but not poised, macrophage-specific enhancers and promoters. The role of ELFs in promoting high-level constitutive transcription was suggested by multiple evidence: ELF sites enabled robust transcriptional activation by endogenous and minimal synthetic promoters, ELF recruitment was stabilized by the transcriptional machinery, and ELF proteins mediated recruitment of transcriptional and chromatin regulators to core promoters. These data suggest that the co-optation of a limited number of highly active transcription factors represents a broadly adopted strategy to equip both cell type-specific and housekeeping cis-regulatory elements with the ability to efficiently promote transcription.