Sedlin controls the ER export of procollagen by regulating the Sar1 cycle.

Newly synthesized proteins exit the endoplasmic reticulum (ER) via coat protein complex II (COPII) vesicles. Procollagen (PC), however, forms prefibrils that are too large to fit into typical COPII vesicles; PC thus needs large transport carriers, which we term megacarriers. TANGO1 assists PC packing, but its role in promoting the growth of megacarriers is not known.

A 14-3-3γ dimer-based scaffold bridges CtBP1-S/BARS to PI(4)KIIIβ to regulate post-Golgi carrier formation.

Large pleiomorphic carriers leave the Golgi complex for the plasma membrane by en bloc extrusion of specialized tubular domains, which then undergo fission. Several components of the underlying molecular machinery have been identified, including those involved in the budding/initiation of tubular carrier precursors (for example, the phosphoinositide kinase PI(4)KIIIβ, the GTPase ARF, and FAPP2), and in the fission of these precursors (for example, PKD, CtBP1-S/BARS). However, how these proteins interact to bring about carrier formation is poorly understood.