sentences:  This promotes ADP-ribosylation of PI31 by the PARP domain of TNKS.In addition, it was shown that treatment of "Drosophila" cells with a TNKS inhibitor, XAV939, attenuated 26S proteasome activity.Moreover, ADP-ribosylation of PI31 has been demonstrated to block PI31-mediated inhibition of α-subunits of the 20S particle.