Figure 4.

Split thymidine kinase reporter gene for imaging of protein-protein interaction. A. Simplified schematic diagram representing the forward or 'folding' mechanism underlying a proteinfragment complementation assay (PCA). B. Transaxial tomographic microPET images through a representative prone-positioned mouse implanted subcutaneously over the left shoulder with mock-transfected 293T cells, and over the right shoulder with 293T cells stably expressing both nTK(V119C)-FRB and FKBP12-cTK. The mouse was injected with 200 μCi of [18F]-FHBG before imaging on days 1, 2 and 5 into the imaging protocol (that is, after 7 d of initial xenograft growth). Elliptical dotted white line outlines the surface of the mouse's upper thorax. Color intensity is a reflection on probe accumulation after its phosphorylation by the complemented thymidine kinase enzyme. Reproduced with permission from ref. 78.