  We calculate the microwave spectra of ultracold KRb alkali metal dimers,
including hyperfine interactions and in the presence of electric and magnetic
fields. We show that microwave transitions may be used to transfer molecules
between different hyperfine states, but only because of the presence of nuclear
quadrupole interactions. Hyperfine splittings may also complicate the use of
ultracold molecules for quantum computing. The spectrum of molecules oriented
in electric fields may be simplified dramatically by applying a simultaneous
magnetic field.
