  We give two graph theoretical characterizations of tope graphs of (complexes
of) oriented matroids. The first is in terms of excluded partial cube minors,
the second is that all antipodal subgraphs are gated. A direct consequence is a
third characterization in terms of zone graphs of tope graphs.
  Further corollaries include a characterization of topes of oriented matroids
due to da Silva, another one of Handa, a characterization of lopsided systems
due to Lawrence, and an intrinsic characterization of tope graphs of affine
oriented matroids. Furthermore, we obtain polynomial time recognition
algorithms for tope graphs of the above and a finite list of excluded partial
cube minors for the bounded rank case. In particular, this answers a relatively
long-standing open question in oriented matroids. Another consequence is that
all finite Pasch graphs are tope graphs of complexes of oriented matroids,
which confirms a conjecture of Chepoi and the two authors.
