A pair of interdigitated gates, interlacing off center, is used to generate a widely tunable one-dimensional lateral superlattice in the two-dimensional electron gas at a GaAs/AlGaAs heterointerface. Magnetotransport measurements with statically biased gates demonstrate that the conduction-band modulation is strongly influenced by higher harmonics, thus allowing the realization of both symmetric and ratchet-like periodic potential modulations. Temporally phase-shifted ac biasing of the gates results in adiabatic pumping of electrons. The generated dc current increases linearly with the pumping frequency and can be reversed in situ by inverting the phase shift.