text: ArcB consists of 778 amino acids. It is a multipass transmembrane protein that passes through the inner membrane twice. The majority of the secondary structure of ArcB is alpha helices; five alpha helices and one beta sheet. The two transmembrane portions of the protein are 20 amino acid long alpha helices that are both rich in hydrophobic amino acids. Amino acids 79-778 are cytoplasmic, 93% of the protein is cytoplasmic. Both the sensory and regulator regions of ArcB are present in this cytoplasmic domain.
  ArcA consists of 238 amino acids. This is an oligomeric protein with two identical subunits; each subunit composed of 119 amino acids, five alpha helices, and six beta sheets. Amino acids 134-234 have the DNA binding domain which can activate or suppress gene expression. There are 76 DNA binding sites in the E. coli genome, however, ArcA directly regulates approximately 30 different operons.