| This thesis focuses on the use of genetic footprinting, a novel approach for comprehensive mutagenesis and analysis, to determine the functional organization of the envelope glycoprotein of a retrovirus, Moloney Murine Leukemia virus. Although previous efforts have been successful in revealing the basic functional organization of the envelope protein (Env), the ability to ascribe function to particular features of the protein has been limited by the relatively small numbers of mutations analyzed in comparison to the large size of the protein. To approach the problem of functional analysis from a more global perspective, genetic footprinting was utilized. This approach permits the rapid generation and functional analysis of a large pool of insertion variants of any cloned gene, obviating the need to generate and analyze each mutant individually and therefore greatly expanding the number of mutants that can be included in a single study. Moreover, it allows facile quantitative comparison of the phenotypes of the mutants. A comprehensive pool of insertion variants of the env gene was created by an in vitro transposition reaction. The pool was then subjected, en masse, to two selections for Env function: (1) the expression of the Env protein at the surface of virus producer cells; and (2) the infectivity of virions displaying the mutant Envs. By obtaining data for 378 mutants, each with an insertion at a unique site in the env gene, this approach has allowed function to be ascribed to previously un-mutagenized sequences, thereby extending the results of earlier studies and providing the basis for the more complete functional characterization of the entire protein.; The second part of this thesis describes the development of a novel retroviral expression system for identifying small molecule inhibitors of signal transduction pathways from randomized pools of retrovirally-expressed peptides. This system has been used to identify peptide inhibitors of apoptosis. |
