| MUL and USP 7 are capable of binding in vitro via their TDs to all of the previously identified TRAF family proteins ( TRAF 1 , TRAF 2 , TRAF 3 , TRAF 4 , TRAF 5 , and TRAF 6 ) , whereas the TD of SPOP interacts weakly with TRAF 1 and TRAF 6 only . ^^^ |