  We use the 1/$N$ expansion formalism in a systematic study of high-spin
states in the $sd$ and $sdg$ boson models with emphasis on spin dependence of
moment of inertia and E2 transitions. The results are applied to the high-spin
states in the actinide nuclei $^{232}$Th, $^{234-238}$U, where the need for $g$
bosons is especially acute but until now, no realistic calculation existed. We
find that the $d$-boson energy plays a crucial role in description of the
high-spin data.
