Cartan subalgebras and the UCT problem

We show that a separable, nuclear C*-algebra satisfies the UCT if it has a Cartan subalgebra. Furthermore, we prove that the UCT is closed under crossed products by group actions which respect Cartan subalgebras. This observation allows us to deduce, among other things, that a crossed product O2⋊αZp satisfies the UCT if there is some automorphism γ of O2 with the property that γ(D2)⊆O2⋊αZp is regular, where D2 denotes the canonical masa of O2. We prove that this condition is automatic if γ(D2)⊆O2⋊αZp is not a masa or α(γ(D2)) is inner conjugate to γ(D2). Finally, we relate the UCT problem for separable, nuclear, M2∞-absorbing C*-algebras to Cartan subalgebras and order two automorphisms of O2.