Vesicle Traffic at Cytokinesis 295
the otherNPSN1families are all phenotypically normal (L. Kong and AAS,
unpublished data), suggesting a strong redundancy among the members of
this gene family. With a Qb-SNARE in hand, a Qc-SNARE was missing, and
my group has recently shown that a Qc-SNARE called SYP71 can also inter-
act with KNOLLE and is found on the cell plate in dividing cells (L. Conner
and AAS, unpublished data). Again, SYP71 is also expressed in non-dividing
cells, and is found on the PM and endosomes in these cells (L. Conner and
Fig. 2The SNARE hypothesis and relevance to cell plate formation.AIn the well-studied
fusion of synaptic vesicles, the Qa-SNARE syntaxin 1 is regulated by association with
the SM-family protein Sec1. Once free from Sec1, Syntaxin binds to the Qb + c-SNARE
SNAP25, forming the pre-synaptic membrane t-SNARE complex. The R-SNARE Synap-
tobrevin is found on the synaptic vesicle, and when triggered for fusion, coils into the
t-SNARE complex, pulling the vesicle membrane close to the synaptic membrane, and
likely driving fusion. Many other factors are involved (not shown), see text for details.
BThe equivalent SNARE complexes for the cell plate include the Qa-SNARE KNOLLE,
the SM-protein KEULE, the Qb + c-SNARE SNAP33; there is also a second complex made
from Qa-KNOLLE, Qb-NPSN11 and the Qc-SYP71. The R-SNARE for either of these two
complexes is unknown, yet is expected to be one of the many members of the R-VAMP72
clade. See text for details and references