Biosynthesis and Intracellular Transport of Ia Antigens

Abstract

Cellular organelles play a major role in the structural and functional organisation of eucaryotic cells. How these organelles are formed, how their specific membrane proteins are inserted and why these proteins are mainly found in one organelle and not in another is the subject of intensive research (Simons and Warren, 1983; Brown et al., 1983; Sabatini et al., 1982; Dobberstein et al., 1982; Kondor-Koch et al., 1982; Bretscher et al., 1980). Proteins destined for the plasma membrane such as the histocompatibility antigens or the glycoprotein of Semliki Forest or Vesicular stomatitis virus, are first inserted into the membrane of the endoplasmic reticulum. They are subsequently transported to the Golgi complex where their carbohydrate side chains are modified and ultimately reach the plasma membrane (Rothman, 1981; Garoff et al., 1982; Ploegh et al., 1981; Krangel et al., 1979; Owen et al., 1980; Dobberstein et al., 1982). Proteins destined for other locations such as lysosomal or secretory proteins are first translocated across the membrane of the endoplasmic reticulum as well and then transported to lysosomes or to the extracellular space (see Hasilik, 1980). The endoplasmic reticulum might furthermore be the site of assembly of endogenous proteins of the endoplasmic reticulum, the Golgi complex and other cellular organelles. The question thus arises as to how these proteins are sorted from one another and what the signals are that direct a protein in its destination.