van Heeswijk, Wally C., Wen, Daying, Clancy, Paula, Jaggi, Rene, Ollis, David L., Westerhoff, Hans V., and Vasudevan, Subhash G. (2000) The Escherichia coli signal transducers PII (GlnB) and GlnK form heterotrimers in vivo: fine tuning the nitrogen signal cascade. National Academy of Sciences. Proceedings, 97 (8). pp. 3942-3947.