  We show that the radiative corrections to charged current (CC) nuclear
reactions with an electron(positron) in the final state are described by a
universal function. The consistency of our treatment of the radiative
corrections with the procedure used to extract the value of the axial coupling
constant $g_A$ is discussed. To illustrate we apply our results to
(anti)neutrino deuterium disintegration and to $pp$ fusion in the sun. The
limit of vanishing electron mass is considered, and a simple formula valid for
$E_{obs}\gsim 1$ MeV is obtained. The size of the nuclear structure-dependent
effects is also discussed. Finally, we consider CC transitions with an
electron(positron) in the initial state and discuss some applications to
electron capture reactions.
