  The particle-number conserving (PNC) method in the framework of cranked shell
model (CSM) is developed to deal with the reflection-asymmetric nuclear system
by applying the $S_x$ symmetry. Based on an octupole-deformed Nilsson
potential, the alternating-parity bands in \element{236,238}{U} and
\element{238,240}{Pu} are investigated. The experimental kinematic moments of
inertia (MoI) and the angular momentum alignments of all studied bands are
reproduced well in the PNC-CSM calculations. The striking difference of
rotational behaviors between U and Pu isotopes can be linked to the strength of
octupole correlations. The upbendings of the alternating-parity bands
in\element{236,238}{U} are due to the alignments of pairs of nucleons occupying
$\nu g_{9/2}$, $\pi f_{7/2}$ orbitals and $\nu j_{15/2}$, $\pi i_{13/2}$
high-$j$ intruder orbitals. Particularly, the interference terms of nucleon
occupying the octupole-correlation pairs of $\nu^2 j_{15/2} g_{9/2}$ and of
$\pi^2 i_{13/2} f_{7/2}$ give a very important contribution to the suddenly
gained alignments.
