Nonpolar virB mutants of Agrobacterium tumefaciens were tested for RSF
1010 mobilization and extracellular complementation. virB2 to virB11 w
ere essential for transfer in both assays. PirB1 was essential only fo
r high frequency transfer of RSF1010 and VirE2. Coordinated transfer o
f a preassembled T complex is supported by these data and competition
studies.