We have compared the behavior of wild-type mouse NEDD-2, a neural precursor cell-expressed, developmentally down-regulated cysteine protease gene, to various mutant forms of the gene in both apoptotic activity in neuronal cells and proteolytic cleavage in the Semliki Forest virus and rabbit reticulocyte protein expression systems. Our results confirm that NEDD-2 processing and apoptotic activity are linked phenomena. They identify aspartate residues as likely targets for autocatalytic cleavage. They establish that cleavage events only occur at specific sites. Finally, they pinpoint differential effects of individual mutations on the overall proteolytic cleavage patterns, raising interesting questions related to the mechanisms of subunit assembly.

Lymphocyte cultures from all normal human adults are stimulated by zinc ions to increase DNA and RNA synthesis and undergo blast transformation. Optimal stimulation occurs at 0.1 mM Zn ++ . Examination of the effects of other divalent cations reveals that 0.01 mM Hg ++ also stimulates lymphocyte DNA synthesis. Ca ++ and Mg ++ do not affect DNA synthesis in this culture system, while Mn ++ , Co ++ , Cd ++ , Cu ++ , and Ni ++ at concentrations of 10 -7 –10 -3 M are inhibitory. DNA and RNA synthesis and blast transformation begin to increase after cultures are incubated for 2–3 days with Zn ++ and these processes reach a maximum rate after 6 days. The increase in Zn ++ -stimulated lymphocyte DNA synthesis is prevented by rendering cells incapable of DNA-dependent RNA synthesis with actinomycin D or by blocking protein synthesis with cycloheximide or puromycin. Zn ++ -stimulated DNA synthesis is also partially inhibited by 5'-AMP and chloramphenicol. Zn ++ must be present for the entire 6-day culture period to produce maximum stimulation of DNA synthesis. In contrast to its ability to independently stimulate DNA synthesis, 0.1 mM Zn ++ inhibits DNA synthesis in phytohemagglutinin-stimulated lymphocytes and L1210 lymphoblasts.