  We perform the BFV-BRST quantization of the fourth-order Pais-Uhlenbeck
oscillator (PUO). We show that although the PUO is not naturally constrained in
the sense of Dirac-Bergmann, it is possible to profit from the introduction of
suitable constraints in phase space in order to obtain a proper BRST invariant
quantum system. Starting from its second-class constrained system description,
we use the BFFT conversional approach to obtain first-class constraints as
gauge symmetry generators. After the Abelianization of the constraints, we
obtain the conserved BRST charge, the corresponding BRST transformations and
proceed further to the BFV functional quantization of the model. We show that
different possible gauge choices can be connected by finite field-dependent
BRST transformations.
