Molecular aspects of the endocytic pathway

Observation of the flow of material along the endocytic pathway has lead to the description of the basic architecture of the pathway and provided insi ght into the relationship between compartments. Significant advances have b een made in the study of endocytic transport steps at the molecular level, of which studies of cargo selection, vesicle budding and membrane fusion ev ents comprise the major part. Progress in this area has been driven by two approaches, yeast genetics and in vitro or cell-free assays, which reconsti tute particular transport steps and allow biochemical manipulation. The com plex protein machineries that control vesicle budding and fusion are signif icantly conserved between the secretory and endocytic pathways such that pr oteins that regulate particular steps are often part of a larger family of proteins which exercise a conserved function at other locations within the cell. Well characterized examples include vesicle coat proteins, rabs (smal l GTPases) and soluble N-ethylmaleimide-sensitive fusion protein (NSF) atta chment protein (SNAP) receptors (SNAREs). Intracompartmental pH, lipid comp osition and cytoskeletal organization have also been identified as importan t determinants of the orderly flow of material within the endocytic pathway .