Evolution and nucleosynthesis in massive stars of zero metallicity

We follow the evolution of rotating, zero metallicity stars in the mass range 15 - 250 M. from the zero-age main sequence to core collapse. Detailed nucleosynthesis is computed using a 199 isotope network complete up to germanium. In addition to the expected overabundance of alpha-isotopes in the final yields (compared to similar mass stars of solar metallicity), we find evidence for the production of primary N-14. Stars more massive than greater than or similar to 100 M. on the main sequence will encounter the electron-positron pair instability following helium burning. For currently favored values of nuclear cross sections and convection algorithm, we determine critical helium core masses for pulsational pair instability, prompt explosion, or prompt black hole formation of 45, 65, and 140 M. respectively. Towards the upper end of the mass range that explodes, very large quantities of Ni-56 produced and the explosion should be extremely bright. The high mass models that make black holes might be potential progenitors of gamma-ray bursts (GRB) of enormous energy.