Confocal images of bimolecular fluorescence complementation (BiFC) studies. The micrographs show a positive result (HSP90 dimerization; ) as well as a negative result (expected absence of interaction between HSP90 and importinα, a mediator of nuclear transportation) of the BiFC assay. HSP90 tagged with the N-terminal fragment of YFP (HSP90-YN) was co-expressed in Nicotiana benthamiana leaves by Agrobacterium tumefaciens transient transformation with the C-terminal fragment of YFP fused to either HSP90 (YC-HSP90; left side) or importinα (YC-IMP; right side). Yellow colour results from the functional complementation of the two halves of the YFP fluorophore and indicates interaction of corresponding fusion proteins. Size bar, 10 μm.