  We discuss the evolution of linear perturbations in a quintessence model in
which the scalar field is non-minimally coupled to cold dark matter. We
consider the effects of this coupling on both cosmic microwave background
temperature anisotropies and matter perturbations. Due to the modification of
the scale of cold dark matter as $\rho_{c} = \rho_{c}^{(0)} a^{-3 + \xi}$, we
can shift the turnover in the matter power spectrum even without changing the
present energy densities of matter and radiation. This can be used to constrain
the strength of the coupling. We find that the phenomenology of this model is
consistent with current observations up to the coupling power $n_{c} \leq 0.01$
while adopting the current parameters measured by WMAP. Upcoming cosmic
microwave background observations continuing to focus on resolving the higher
peaks may put strong constraints on the strength of the coupling.
