Figure 1.

Schemes of intra-Golgi transport (IGT). ((I): (A–O)) Mechanisms of IGT according to the cisterna maturation–progression model of intracellular Golgi transport (CMPM; see Movie S1). (A) Two ER-Golgi carriers (EGCs) are shown in the upper part of the Figure. They contain mega-cargo (blue lines) and soluble secreftory cargo (red dots). (B) These carriers arrive on the opposite side of the Golgi complex. (C) The EGCs fuse and form a new cis-cisterna that contains these mega- and soluble cargoes. Coatomer I (black dots) forms coats on cisternal rims. (D) Formation of COPI-coated buds on rims of all of the Golgi cisternae. These buds are enriched in Golgi glycosylation enzymes corresponding to the positions of the cisternae on which they are formed. (E) Division of the copy-covered kidneys. During division, these buds turn into ‘bubbles’ enriched with Golgi enzymes and then undergo coat removal. (F) Fusion of COPI-dependent vesicles with proximal cisterna. Recycling of Golgi enzymes into the corresponding proximal cisterna. (G) Attachment of COPI to the rims of the cisternae. (H) Arrival of new ER-Golgi carriers and formation of a new cis-cisterna, as well as fission of the neck of COPI-coated buds and division of bubbles, and formation of an empty trans-cisterna. (I) Merging of carriers to form a new cis- cisterna. Fusion of COPI-dependent vesicles with proximal cisternae and formation of two carriers after the Golgi from an empty trans-cisterna. (J–O) Two consecutive rounds of the same process that occurs distally along the Golgi stack. As a result, the cis- cisterna containing the mega-cargo (blue lines) and soluble cargo (red dots) appears on the trans-position within the stack. ((II): (A–F)) Mechanisms of concentration of soluble cargoes according to the symmetric KARM (the carrier maturation model). Black dots, soluble cargo; red dots, proton pumping inside the distal compartment. The soluble cargo can diffuse in both directions through a thin tube connecting the two compartments. In the bottom part of the distal compartment, there is a proton pump ((A); square), which moves protons into the lumen of the distal compartment (B). When a proton attaches to the cargo, the cargo molecule tends to form aggregates (C,D). Aggregates become larger than the original molecule and cannot move through the tubes in the retrograde direction. After several cycles of such transformation (E), the concentration of the cargo in the distal compartment becomes higher than in the proximal compartment (F).