The full-length Sec7 functions proximally in the secretory pathway as a protein binding scaffold for the coat protein complexes COPII-COPI. The COPII-COPI-protein switch is necessary for maturation of the vesicular-tubular cluster, VTC, intermediate compartments for Golgi compartment biogenesis. This N-terminal domain however does not appear to be binding either of the COP or the ARF [2]. This is the HUS (homology upstream of Sec7) domain of Sec7 and related proteins such as protein Mon2 and BIG1-like proteins, which plays a regulatory role [3,4] together with DCB domain (Pfam:PF16213).

1: SEC7 encodes an unusual, high molecular weight protein required for membrane traffic from the yeast Golgi apparatus. Achstetter T, Franzusoff A, Field C, Schekman R; J Biol Chem. 1988;263:11711-11717. PMID:3042778

2: Sec7p directs the transitions required for yeast Golgi biogenesis. Deitz SB, Rambourg A, Kepes F, Franzusoff A; Traffic. 2000;1:172-183. PMID:11208097

3: Structural Insights into Arl1-Mediated Targeting of the Arf-GEF BIG1 to the trans-Golgi. Galindo A, Soler N, McLaughlin SH, Yu M, Williams RL, Munro S; Cell Rep. 2016;16:839-850. PMID:27373159

4: The Sec7 N-terminal regulatory domains facilitate membrane-proximal activation of the Arf1 GTPase. Richardson BC, Halaby SL, Gustafson MA, Fromme JC; Elife. 2016; [Epub ahead of print] PMID:26765562