Expression of soluble NifB candidates in mitochondria and chloroplasts. Immunoblot analysis of soluble N. benthamiana protein extracts with antibodies against the TS-tag (α-Strep, for NifB detection), GFP, NifU, NifS, and the HA tag (for FdxN detection). “Ctrl (–)” indicates total protein extract from nontransformed tobacco leaves. “A.v. CFE” is A. vinelandii soluble protein extract used as a control for the migration of NifU and NifS. The black arrow indicates NifBMt; the green arrows indicate NifU and NifS.