You are a researcher working on the structure of the human proteasome, the main protein degradation machinery of the cell. You are specially interested in knowing if the subunits B5 (UniProtKB id PSB5_HUMAN) and A7 (UniProtKB id PSA7_HUMAN) of the proteasome have been reported to be directly linked or if they are linked through a third protein. You also want to know if the interactions found have been proved to be binary interactions between the proteins involved.
Use IntAct to look for interacting partners of the proteasome subunits B5 and A7. Find out if the two proteins interact or if there are other proteins acting as linkers between them. Filter out any interactions from your results that are not binary.