  We investigate a cosmological model in which dark energy, represented by a
quintessential scalar field, is coupled to a dark-matter perfect fluid in the
spatially flat Friedmann-Robertson-Walker Universe. This allows an energy
exchange in the dark sector which could happen both at early times before
recombination era or at late times. We use the coupling function
$Q=\gamma\rho_{dm}\dot{\varphi}$ which is induced by conformal transforming
scalar-tensor and $f(R)$ gravity theories to Einstein frame. It is argued that
there is a connection between this coupling function and $Q\propto \rho_{dm}H$.
A dynamical analysis is used to show that there are early- and late-time
attracting solutions for which the system evolves for a wide range of initial
conditions. These attractors generalize the scaling solutions which have been
already found in the non-interacting case.
