ER-associated retrograde SNAREs and the Dsl1 complex mediate an alternative, Sey1p-independent homotypic ER fusion pathway.
Bottom Line: However, an alternative explanation--that the observed phenotypes arose from perturbed vesicle trafficking--could not be ruled out.In contrast, cytosolic coat protein I (COPI) vesicle coat mutations in sey1Δ cells caused no synthetic defects, excluding perturbed retrograde trafficking as a cause for the previously observed synthetic defects.We conclude that the ER SNAREs and the Dsl1 complex directly mediate Sey1p-independent ER-ER fusion and that, in the absence of both pathways, cell viability depends upon membrane curvature-promoting reticulons.
Affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014.Show MeSH
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Mentions: To identify the most informative genetic interactions, we grouped the interactions into three classes: interactions shared between dsl1ΔE and dsl1ΔL, dsl1ΔL-specific interactions, and dsl1ΔE-specific interactions (Figure 2A; full data set available in Supplemental Table S1; classes determined via a cutoff score and a difference threshold; see Materials and Methods). As expected, the strongest interactions shared between dsl1ΔE and dsl1ΔL consisted of known components of vesicle trafficking. In the dsl1ΔL-specific class, we identified five negative interactions: pse1-41, hir1Δ, mps3-1, chk1Δ, and cse2Δ. Four of these genes have nuclear roles: Pse1p interacts with nuclear pore complexes, Mps3p resides at the half-bridge and mediates spindle pole body formation, Hir1p is a subunit of the histone regulation complex, and Cse2p is a subunit of the RNA polymerase II mediator complex. Interestingly, while pse1-41 is by far the strongest dsl1ΔL-specific negative genetic interaction, pse1-34 is among the strongest dsl1ΔL-specific positive interactions. The final interaction, chk1Δ, uniquely interacts both negatively with dsl1ΔL and positively with dsl1ΔE. Chk1p is a checkpoint kinase that mediates cell cycle arrest.
Affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014.