(G). GFP-tagged ERMES complex proteins retain their characteristic punctate structure in Δlam6, suggesting that Lam6 is not an essential complex member. Scale bar represents 5 μm.

(A) Fluorescence microscopy demonstrates that Lam6-GFP co-localizes with ERMES (Mdm34-Cherry) (yellow arrows) and also localizes to non-ERMES locations in the cell (red arrows). These additional locations co-localized with the NVJ (Nvj1-GFP) as well as with the vCLAMP (GFP-Vps39). Scale bar represents 5 μm.(B) Overexpression and tagging of Lam6 confirmed that it co-localizes with ERMES (Mdm34-GFP) (yellow arrows) as well as to additional contact sites (red arrows), NVJ (marked by Nvj1) and vCLAMP (marked by Vps39). Scale bar represents 5 μm.(A) Fluorescence microscopy demonstrates that the overexpression of Cherry-Lam6 (OE-Cherry-LAM6) results in an expansion of the following three contact sites: ERMES (Mdm34-GFP), NVJ (Nvj1-GFP), and vCLAMP (GFP-Vps39). This suggests that an increase in Lam6 levels in the contact site is sufficient for its expansion. The numbers represent the average contact site size (120 cells per sample). Scale bar represents 5 μm.(B) Immuno-EM verified that GFP-Lam6 overexpression indeed causes an expansion of contact site size. While vCLAMP was hardly visible in WT cells, it could be detected easily in the OE strain (albeit often had ER tubules invading it). The NVJ underwent expansion as well as evoked PMN in OE strains, and the ER-mitochondria contact became large and elongated instead of small and distinct. N, nucleus; M, mitochondria; V, vacuole. Scale bar represents 200 nm (see also Figure S3I).

(A) Fluorescent microscopy shows that the ERMES contact (as measured by the number of Mdm34-GFP puncta per cell) expanded in the Δvps39 background relative to WT. However, the expansion did not occur on the background of Δvps39 Δlam6, demonstrating that Lam6 is necessary for ERMES expansion under these conditions. Scale bar represents 5 μm.

(B) Quantitation of (A). Bars represent the percentage of cells containing the specific number of puncta/cell out of total cells counted for the strain (for WT, n = 234 cells; for Δvps39, n = 246; for Δvps39 Δlam6, n = 271).

(C) Fluorescent microscopy demonstrates that downregulating ERMES contacts (by growing GALp-MDM34 strains in glucose) indeed caused expansion of vCLAMP (GFP-Vps39). However, this expansion was diminished in a Δlam6 background. Scale bar represents 5 μm (see also Figure S4).