The long-term objectives of this research program are to explore the molecular bases of a number of different cellular phenomena, all of which have in common the involvement of cell membranes. The specific problems to be investigated, which are outgrowths of our past studies on this grant, include the following: 1) the mechanisms of intracellular transport of secretory and integral membrane proteins from the endoplasmic reticulum to the Golgi apparatus; 2) the role of newly discovered membrane-bound tyrosin kinases, which are prominent components in the chick embryo, in embryonic development; 3)the mechanisms of signal transduction across membranes that result in massive cytoplasmic rearrangements and polarization inside the affected cells.