COMMUNICATION OF CLPXP PROTEASE HYPERSENSITIVITY TO BACTERIOPHAGE-MU REPRESSOR ISOFORMS

The immunity repressor (Rep) of bacteriophage Mu establishes and maint ains lysogeny by shutting down transposition functions needed for phag e DNA replication. Although Rep is stable in vivo, an altered immunity repressor (Vir) encoded by virulent, trans-dominant Mu mutants is rap idly degraded by Escherichia coli ClpXP protease. Rep and Vir are degr aded at approximately the same maximal velocity (V-max) by ClpXP, but the K-m for Rep (3.6 mu M) is over 20-fold higher than the K-m for Vir (0.15 mu M) Rep is also highly resistant to degradation in the presen ce of DNA whereas Vir is not. Vir increases the rate of Rep degradatio n by reducing its K-m and imparts to Rep ClpXP sensitivity in the pres ence of DNA. Vir can drive at an accelerated rate the complete degrada tion of Rep molecules that outnumber Vir by eightfold or more. So long as Vir is present at a concentration of 0.1 mu M or higher, Rep is de graded with a K-m that is indistinguishable from that of Vir. These ch aracteristics of repressor may be an important means of transducing ph ysiological signals that induce Mu transposition in response to growth conditions or environmental stress, ClpXP hypersensitivity being diss eminated among Rep molecules for the induction of Mu transposition. (C ) 1997 Academic Press Limited.