IN forms the structural core of the PIC and is almost certainly associated with PIC migration ubiquitin-conjugating along microtubules, shift to the nucleus, as well as integration and chromatin targeting. Comparison of known components of retroviral INs shows the high conformational flexibility of its different domains, with respect to the virus type and the clear presence of connecting host proteins. That conformational mobility explains the power of INTO connect to multiple partners and to exert multiple biological functions. To achieve further insight in to the regulation of IN functions by host facets, we investigated the structures and connections of IN with the cellular LEDGF and INI1 IBD proteins, as well as their impact on activities. The IN/LEDGF complex was founded to be composed of 4 IN and hematopoietin 2 LEDGF molecules but little information was on the binding of viral DNA. Based on a perfection research, FCS suggests that two U5 viral DNA duplexes can bind to the complex. Furthermore, the diffusion constant calculated by FCS for the IN/LEDGF/vDNA complex is in line with the theoretical diffusion constant of the IN4 LEDGF2 vDNA2 complex, calculated from its dimensions determined by EM. Hence, FCS confirms that IN4 LEDGF2 vDNA2 is the complex in solution. The addition of INI1 IBD to IN/LEDGF light emitting diode to a reliable IN/LEDGF/INI1 IBD complex which suggests that both cellular proteins can bind simultaneously to IN. By further adding U5 vDNA duplex, an IN/LEDGF/INI1 IBD/vDNA complex was created ergo showing that neither host element disrupts vDNA binding. Fluorescence anisotropy confirms that U5 vDNA duplexes bind exclusively to both IN/LEDGF and IN/LEDGF/INI1 IBD complexes, with affinities of 35 nM and 11, respectively. Celecoxib Ergo, INI1 IBD only weakly influences the binding of vDNA towards the complex. The Cryo EM structure of the IN/LEDGF/INI1 IBD/vDNA complex completely agrees with the stoichiometry of 4 IN, 2 LEDGF, 2 INI1 IBD and 2 vDNA substances based on FCS and mass spectrometry and moreover reveals the interaction sites of LEDGF, INI1 IBD and vDNA with IN. INI1 IBD interacts mainly with the C terminal domains of two IN monomers and with the N terminal domain of monomer B. In this position INI1 IBD does not sterically hinder the DNA binding site of IN which seems occupied in the 3 D model as predicted by the binding studies. The general domain business of the IN tetramer in complex with DNA, LEDGF and INI1 IBD is comparable to of the one found in the absence of INI1 except for conformational changes in the D and C terminal areas of IN due to their interactions with INI1 IBD. These interactions stabilize an IN conformation that’s maybe not suitable for the integration reaction and 39 processing. Specifically, the reorientation of the N and C terminal elements of IN induces a rotation of approximately 40u of the viral DNA as compared to the previously examined 39 processing complex.