We intend to continue our investigation of the role of the products of glnA, glnB, glnF and glnG genes of enteric organisms in the regulation of the synthesis of glutamine synthetase. We shall continue our study of the regulation of nitrogen metabolism of Saccharomyces cerevisiae in particular by the isolation and investigation of mutants with altered sensitivity of glutamine synthetase formation and the formation of the proline permeases to repression by ammonia.