Transcription factor MotA is required for the activation of middle promoters in Bacteriophage T4, in addition to phage T4 co-activator AsiA, and sigma-70-containing Escherichia coli RNA polymerase. Phage T4 middle promoters have the sigma70 -10 DNA element, but not the -35 element; instead, they have a MotA box at -30 to which the transcription factor MotA binds . MotA and AsiA interact with the C-terminal of sigma70 (region 4), which normally binds the -35 element and the beta-flap, thereby diverting sigma70 away from host promoters that require -35 element-binding to phage T4 middle promoters.
Transcription factor MotA has two domains: an N-terminal domain required for binding to sigma70, and a C-terminal domain required for binding to the -30 MotA box element in the phage T4 middle promoter. This entry represents the C-terminal domain of MotA factors, which adopts a compact alpha/beta structure comprising three alpha-helices and six beta-strands in the order: alpha1-beta1-beta2-beta3-beta4-alpha2-beta5-beta6-alpha3. In this architecture, the domain's hydrophobic core is at the sheet-helix interface, and the second surface of the beta-sheet is completely exposed. It contains a DNA-binding motif, with a consensus sequence containing nine base pairs (5'-TTTGCTTTA-3'), that appears to bind to various mot boxes, allowing access to the minor groove towards the 5'-end of this sequence and the major groove towards the 3'-end .