Characterizing protein mobility and interaction in vivo is a challenging problem, highly relevant for understanding biological function. Here we present first results from a 2D-parallel fluorescence (cross) correlation (F(C)CS) technique using single plane illumination microscope (SPIM). The goal is to understand the function of transcription factors (TFs) through their localization, binding dynamics and transport to their sites of action in the cell nucleus. Our model system is the well-known TF pair c-Fos and c-Jun, which form a heterodimer and participate in proliferation, differentiation, apoptosis, and oncogenesis. using autofluorescent proteins such as GFP and mRFP, the interaction between these TFs in living cells can be quantified by F(C)CS.Our SPIM uses as detector either an electron multiplying CCD (EM-CCD) camera or a newly developed array of avalanche photodiodes with a time resolution of 10 μs per frame on 32x32 pixel images. By expansion of the single color to two color detection with the use of a second laser and dual-view optics, we can now observe the dynamics and quantify the interaction of c-Fos-GFP and c-Jun-mRFP proteins across an entire living cell. The results are presented in the form of diffusion and concentration maps, characterizing for the first time directly in vivo the action of c-Fos and c-Jun throughout the entire nucleus. This yields important new information about the spatiotemporal organization of c-Fos and c-Jun.