The septation apparatus, an autonomous system in budding
yeast.
Dong-Hyun Roh (1), Blair Bowers (2), Martin Schmidt
(1), Enrico Cabib (1)
(1) LBG, NIDDK, NIH, Building 8 Room 403,
Bethesda, MD 20910-0851, USA; (2) LCB/NHLBI/NIH, Building 50, Bethesda,
MD20892-8017, USA
For an orderly cell division in budding yeast, both
actomyosin ring contraction and septum synthesis must occur
simultaneously. By fluorescence double labeling of Myo1p, as
representative of the contractile ring, and Chs2p for the primary septum
we show that the two processes proceed essentially at the same location
and simultaneously. Chs2p differs from Myo1p in that it reflects the
changes in shape of the plasma membrane to which it is attached and in
that it is packed after its action into visible endocytic vesicles for
its disposal. To ascertain whether this highly coordinated system could
function independently of other cell cycle events, we reexamined the
septum-like structures made by the septin mutant cdc3 at various
sites on the cell cortex at the nonpermissive temperature. We observed
that in cdc3 mutants at nonpermissive temperature both Myo1p and
Chs2p colocalize at different spots of the cell cortex. A contraction of
the Myo1p patch could also be detected, as well as that of a Chs2p
patch, with subsequent appearance of vesicles. Furthermore, the septin
Cdc12p, fused with a fluorescent protein, also colocalized with Myo1p
and Chs2p at the aberrant locations. We conclude that the septation
apparatus, containing septins, contractile ring and the chitin synthase
II system, can function at ectopic locations autonomously and
independently of cell division, and that it can recruit the other
elements necessary for the formation of secondary septa.
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