  Surface electrons of strong topological insulator wires acquire a Berry phase
difference of $\pi$ on orbiting the wire. This can be detected in response of
clean wires (whose Fermi level is tuned to the Dirac point) to the presence of
the Aharonov-Bohm flux. Specifically, at half-odd integer applied flux (in
units of $hc/e$), long wires undergo semimetal-semiconductor transitions
characterized by logarithmically divergent susceptibility. Associated with
these are oscillations of magnetization (persistent current) that vanish both
at integer and half-odd integer flux. Additionally wires of arbitrary aspect
ratio exhibit conductance maxima at half-odd integer applied flux and minima at
integer flux. For long wires the maxima are sharp with their height approaching
$e^{2}/h$. Short wires are characterized by a universal conductivity $e^{2}/\pi
h$ attained in the disc limit.
