  We study the single-transverse spin asymmetry in semi-inclusive hadron
production in deep inelastic scattering. We derive the leading contribution to
the asymmetry at moderate transverse momentum $P_{h\perp}$ of the produced
hadron in terms of twist-three quark-gluon correlation functions, and compare
with the approach based on the factorization at fixed transverse momentum
involving the asymmetric transverse-momentum and spin-dependent quark
distribution. We verify that the two approaches yield identical results in this
regime. By a comparison with our earlier calculations for the single-spin
asymmetry in the Drell-Yan process we recover the well-established
process-dependence of the time-reversal-odd transverse-momentum-dependent quark
distributions that generate single-spin phenomena.
