  We characterize the $L^1(E;\mu_\infty)$-spectrum of the Ornstein-Uhlenbeck
operator, where $\mu_\infty$ is the invariant measure for the
Ornstein-Uhlenbeck semigroup. The main result covers the general case of an
infinite-dimensional Banach space E under the assumption that the point
spectrum of drift operator $A^*$ is nonempty. This extends several recent
related results.
