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* Division of Molecular Medicine, Wadsworth Center, New York State Department of Health, Albany, New York 12201-0509;
and We used laser microsurgery to cut between
the two sister kinetochores on bioriented prometaphase chromosomes to produce two chromosome fragments containing one kinetochore (CF1K). Each of these CF1Ks then always moved toward the spindle
pole to which their kinetochores were attached before
initiating the poleward and away-from-the-pole oscillatory motions characteristic of monooriented chromosomes. CF1Ks then either: (a) remained closely associated with this pole until anaphase (50%), (b) moved
(i.e., congressed) to the spindle equator (38%), where
they usually (13/19 cells) remained stably positioned
throughout the ensuing anaphase, or (c) reoriented and
moved to the other pole (12%). Behavior of congressing CF1Ks was indistinguishable from that of congressing chromosomes containing two sister kinetochores.
Three-dimensional electron microscopic tomographic
reconstructions of CF1Ks stably positioned on the spindle equator during anaphase revealed that the single kinetochore was highly stretched and/or fragmented and
that numerous microtubules derived from the opposing
spindle poles terminated in its structure. These observations reveal that a single kinetochore is capable of simultaneously supporting the function of two sister kinetochores during chromosome congression and imply
that vertebrate kinetochores consist of multiple domains whose motility states can be regulated independently.
Department of Biomedical Sciences, State University of New York, Albany, New York 12201
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