Asparaginyl-tRNA synthetase from Chinese hamster liver will be purified and its properties studied and compared to the properties of the enzyme from wild-type CHO cells and from a mutant with a temperature-sensitive asparaginyl-tRNA synthetase. The in vivo charging levels of the isoaccepting species of tRNAAsn in the mutant and wild-type cells will be determined under permissive and restrictive conditions and will be correlated with the extent of derepression of the biosynthetic asparagine synthetase. The rates of synthesis and degradation of histidase in inbred strains of mice apparently differing in their liver histidase content will be studied in an attempt to determine the biochemical basis for this difference. In vitro studies of histidase degradation will also be undertaken. Biochemical and genetic studies of the basis for the differences in liver ornithine transaminase activity in inbred strains of mice will be started.