  We analyze an interplay between Coulomb blockade and quantum fluctuations in
a coherent conductor (with dimensionless conductance $g \gtrsim 1$) attached to
an Ohmic shunt. We demonstrate that at T=0 the system can be either an
insulator or a metal depending on whether its total resistance is larger or
smaller than $h/e^2\approx 25.8$ k$\Omega$. In a metallic phase the Coulomb gap
is fully suppressed by quantum fluctuations. We briefly discuss possible
relation of this effect to recent experiments indicating the presence of a
metal-insulator phase transition in 2d disordered systems.
