FIG. 1.

Identification of NopB as a TTSS-dependent secreted protein (A) Extracellular proteins of apigenin-induced cultures of Rhizobium sp. strain NGR234 and NGRΩrhcN (a TTSS mutant) were electrophoretically separated by one-dimensional SDS-15% PAGE. Molecular masses of the marker proteins are indicated on the right. The identified Nops are named on the left. A 16-kDa protein labeled as Nop16 was unique to induced wild-type NGR234 and absent in NGRΩrhcN. (B) 2D gel electrophoresis of total extracellular proteins from apigenin-induced cultures of NGR234 (left panel) and NGRΩrhcN (right panel). Each sample contained 75 μg of protein and was IEF for a total of 100,000 Vh. The IPG strips were then placed on top of SDS-12% PAGE gels and after separation were stained with silver nitrate. Black circles indicate the (approximately 16-kDa) protein spots that were subjected to matrix-assisted laser desorption ionization-time of flight mass spectrometry.