  Keldysh representation of the functional integral for the interacting
electron system with disorder is used to derive microscopically an effective
action for dirty superconductors. In the most general case this action is a
functional of the 8 x 8 matrix Q(t,t') which depends on two time variables, and
on the fluctuating order parameter field and electric potential. We show that
this approach reproduces, without the use of the replica trick, the well-known
result for the Coulomb-induced renormalization of the electron-electron
coupling constant in the Cooper channel. Turning to the new results, we
calculate the effects of the Coulomb interaction upon: i) the subgap Andreev
conductance between superconductor and 2D dirty normal metal, and ii) the
Josephson proximity coupling between superconductive islands via such a metal.
These quantities are shown to be strongly suppressed by the Coulomb interaction
at sufficiently low temperatures due to both zero-bias anomaly in the density
of states and disorder-enhanced repulsion in the Cooper channel.
