176 Y.-R.J.Lee·B.Liu
been proved to be associated with chromosomes. It is noteworthy that the ho-
mology of plant kinesins with their animal counterparts in these subfamilies
only limits to their motor domains. Functional non-motor domains found in
animal Kinesin-4, -7, -10, -13 are not detected in the plant members of these
subfamilies.
After the breakdown of the nuclear envelope, kinetochores exhibit a lateral
interaction with microtubules prior to the formation of end-on kinetochore
fibers in plant cells (Liu and Palevitz 1991). Thus, kinesins yet to be identi-
fied may be accountable for bringing kinetochores to plus ends of kinetochore
fiber microtubules. To date, only a soybean kinesin decorates the kinetochore
indicating that plant kinesin(s) do act at the kinetochore (Lee and Liu, unpub-
lished data) (Fig. 3). Whether it plays a role in mitosis awaits further analysis.
Congression of chromosomes to the metaphase plate is a key step at
prometaphase before cells proceed to anaphase. In animal cells, a number of
Fig. 3 Kinesin at the kinetochore.AA metaphase soybean cell was stained for micro-
tubules (red), kinesin (green), and DNA (white). Note the kinesin was detected at the
kinetochore (arrowheads).BDiagram of transition from lateral interaction between mi-
crotubules and the kinetochore to an end-on association. A plus end-directed kinesin is
proposed to play a role in this process.Arrowindicates plus end-directed motility for
bringing chromosomes to the microtubule plus end