  We calculated the effects of structural distortions on the electronic
structure of carbon nanotubes. The key modification of the electronic structure
brought about by bending a nanotube involves an increased mixing of $\sigma$
and $\pi$-states. This mixing leads to an enhanced density-of-states in the
valence band near the Fermi energy region. While in a straight tube the states
accessible for electrical conduction are essentially pure C($2p_{\pi}$)-states,
they acquire significant C($2sp_{\sigma}$) character upon bending. Bending also
leads to a charge polarization of the C-C bonds in the deformed region
reminiscent of interface dipole formation. Scattering of conduction electrons
at the distorted regions may lead to electron localization at low temperatures.
