Transcription factors harbor functional RNA-binding domains

Transcription factors (TFs) orchestrate the gene expression programs that define each cell’s identity, and the canonical TF accomplishes this with two functional domains1–7. The DNA-binding domain interacts with specific genomic sequences, and the effector domain binds coactivators or co-repressors that contribute to transcriptional regulation. We report here that TFs also frequently contain an RNA-binding domain and that this also contributes to gene regulation. Nearly half of TFs in human cells show evidence of RNA-binding and their affinities for RNA are similar to those of well-studied RNA-binding proteins. The RNA-binding sites of TFs have sequence and functional features analogous to the arginine-rich motif of the HIV transcriptional activator Tat8,9. RNA-binding contributes to TF function by promoting the dynamic association of TFs with chromatin. We conclude that the canonical definition of transcription factors is incomplete, and that the ability of many TFs to bind DNA, RNA and protein is fundamental to gene regulation.