Functional determinants of transcription factors in Escherichia coli: protein families and binding sites.

DNA-binding transcription factors regulate the expression of genes near to where they bind. These factors can be activators or repressors of transcription, or both. Thus, a fundamental question is what determines whether a transcription factor acts as an activator or a repressor? Previous research into this question found that a protein's regulatory function is determined by one or more of the following factors: protein-protein contacts, position of the DNA-binding domain in the protein primary sequence, altered DNA structure, and the position of its binding site on the DNA relative to the transcription start site. Although there are many aspects specific to different transcription factors, in this work we demonstrate that, in general, in the prokaryote Escherichia coli, a transcription factor's protein family is not indicative of its regulatory function, but the position of its binding site on the DNA is.