Analysis of nonsense-mediatedmRNA decay in Caenorhabditis elegans

mRNAs that contain premature translation termination codons are unstable in most, if not all, eucaryotes. Functions of the six smg genes are required to degrade nonsense mutant mRNAs in C. elegans. In smg(+) genetic backgrounds, nonsense mutant mRNAs are unstable, and their steady-state levels are severely reduced. In ;Work presented here demonstrates that smg-dependent dominant mutations are remarkably common. Mutations in many different genes are strongly dominant when ;This thesis also describes the identification and molecular characterization of a previously uncharacterized smg gene, smg-7. smg-7 is located downstream of, and likely cotranscribed with, the previously characterized gene lin-45 raf. smg-7 is predicted to encode a novel 53 kilodalton protein with two notable features; three repeats of a conserved type of amphipathic helix (the tetratricopeptide repeat) that likely mediates protein:protein interactions, as well as an acidic COOH-terminus. I also describe production of polyclonal antibodies to SMG-7 and present evidence to suggest SMG-7 is nuclear in the germ-line but localized to the cytoplasm at or shortly after fertilization.;I also report progress towards the cloning of smg-3. smg-3 is located on a 250 kb region of the physical map defined by a single yeast artificial chromosome (YAC) using both restriction-fragment length polymorphism (RFLP) mapping and transformation rescue. Initial results of a chromosome walk to smg-3 are also presented.