trans-Targeting of the Phage Mu Repressor Is
Promoted by Conformational Changes That Expose Its ClpX
Recognition Determinant*
Kimberly R.
Marshall-Batty and
Hiroshi
Nakai
From the Department of Biochemistry and Molecular Biology,
Georgetown University Medical Center, Washington, D. C. 20057
Dominant negative forms of the phage Mu
repressor, including the mutant Vir repressors, are not only rapidly
degraded by the ClpXP protease but also promote degradation of the
unmodified, wild-type repressor. This trans-targeting of
the wild-type repressor depends upon a determinant within its
C-terminal domain, which is needed for recognition by ClpX. An
environmentally sensitive fluorescent probe
(2-(4'-maleimidylanilino)naphthalene-6-sulfonic acid (MIANS)) attached
to the C terminus of the full-length repressor indicated that Vir
induces the movement of this domain into a more exposed configuration.
Vir also promoted attachment of MIANS to the C terminus of the
repressor at an accelerated rate, and it greatly increased the rate of
phosphorylation of a cAMP-dependent protein kinase motif
attached to the repressor C terminus. While an excess of Vir was needed
to promote repressor phosphorylation at maximal rates, the presence of
ClpX could increase phosphorylation rates at lower Vir levels.
trans-Targeting of the Mu repressor is therefore promoted
by exposing its ClpX recognition determinant, and the action of ClpX
can assist Vir in exposing these determinants.
*
This work was supported by National Institutes of Health
Grant GM58265 (to H. N.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.