Melchers LS, Maroney MJ, den Dulk-Ras A, Thompson DV, van Vuuren HA, Schilperoort RA, Hooykaas PJ. Octopine and nopaline strains of Agrobacterium tumefaciens differ in virulence; molecular characterization of the virF locus. Plant Mol Biol. 1990 Feb; 14(2):249-59.