  Magnetic flux rope (MFR) is a coherent and helical magnetic field structure
that is recently found probably to appear as an elongated hot-channel prior to
a solar eruption. In this paper, we investigate the relationship between the
hot-channel and associated prominence through analyzing a limb event on 2011
September 12. In the early rise phase, the hot-channel was cospatial with the
prominence initially. It then quickly expanded, resulting in a separation of
the top of the hot-channel from that of the prominence. Meanwhile, both of them
experienced an instantaneous morphology transformation from a $\Lambda$ shape
to a reversed-Y shape and the top of these two structures showed an exponential
increase in height. These features are a good indication for the occurrence of
the kink instability. Moreover, the onset of the kink instability is found to
coincide in time with the impulsive enhancement of the flare emission
underneath the hot-channel, suggesting that the ideal kink instability likely
also plays an important role in triggering the fast flare reconnection besides
initiating the impulsive acceleration of the hot-channel and distorting its
morphology. We conclude that the hot-channel is most likely the MFR system and
the prominence only corresponds to the cool materials that are collected in the
bottom of the helical field lines of the MFR against the gravity.
