A previous study has shown that YopB of Yersinia spp, is essential for translocation of Yop effectors across the eucaryotic plasma membrane (M.-P. Sory and G, R. Cornelis, Mol. Microbiol. 14:583-594, 1994). Hows, er, this role was recently challenged (V. T. Lee and O. Schneewind, Mol. Microbiol. 31:1619-1629, 1999), Using protease protection and digitonin extraction, me reconfirm that YopB of Yersinia enterocolitica is essential for the translocation of YopE into HeLA cell monolayers.