Regis B. Kelly

Protein secretion from cells can take several forms. Secretion is constitutive if proteins are secreted as fast as they are synthesized. In regulated secretion newly synthesized proteins destined for secretion are stored at high concentration in secretory vesicles until the cell receives an appropriate stimulus. When both constitutive and regulated protein secretion can take place in the same cell a mechanism must exist for sorting the correct secretory protein into the correct secretory vesicle. The secretory vesicle must then be delivered to the appropriate region of plasma membrane. Transfection of DNA encoding foreign secretory proteins into regulated secretory cells has provided insight into the specificity of sorting into secretory vesicles.

SORTING 257 CYTOSKELETON INVOLVEMENT WITH PROTEIN SECRETION 266 SECRETION IN EPITHELIAL CELLS .... 277 RECYCLING OF THE SECRETORY VESICLE MEMBRANE ..... . . 281

The endocytosis process is of critical importance for a variety of cellular life functions. Vesicle formation during receptor-mediated endocytosis involves a complex protein machinery and additional proteins to control it. Although our understanding of this endocytic machinery has grown rapidly

Abstract Double stranded DNA serves as a template primer for Escherichia coli DNA polymerase when the DNA contains a single strand break (a nick) with a 3'-hydroxyl terminus. Initiation of replication entails covalent extension of the 3'-hydroxyl terminus and a concurrent 5' → 3' nuclease action by the enzyme. The primer strand is hydrolyzed at the 5' side of the nick while the synthetic activity catalyzes the addition of nucleotides to the 3' side. The ability of the enzyme to promote hydrolysis and synthesis simultaneously results in the translation of the nick along the DNA duplex in the 5' to 3' direction. The mechanism for conserving the 5'-strand and providing net synthesis of DNA in later phases of the reaction has not yet been clarified.