Activates the transcription of the eut operon. Also positively regulates its own transcription. Probably binds ethanolamine and vitamin B12 as effectors. Competes with ethanolamine ammonia-lysase (EAL, the first enzyme in the EA degradation pathway) for adenosylcobalamin. Amine and polyamine degradation; ethanolamine degradation. In strain MG1655 the eut operon is interrupted by the CPZ-55 prophage, encoding 9 genes situated between eutA and eutB, which are translated in the other direction. CPZ-55 may prevent expression of the eut operon in strain MG1655. Strain W3110 does not have this prophage element and should be able to express the operon.