Glutamine Synthetase and the Regulation of Histidase Formation in Klebsiella aerogenes

Abstract

Abstract It has been shown previously that histidase and proline oxidase of Klebsiella typhimurium escape from the catabolite repression exerted by glucose when the source of nitrogen is growth rate-limiting. We have now found that this escape is related to the cellular level of glutamine synthetase. In cells growing with an excess of ammonia, the level of glutamine synthetase is low, whereas in cells growing on a growth rate-limiting nitrogen source the level of glutamine synthetase is high. Mutations at two chromosomal sites, glnA and glnB result in the loss of glutamine synthetase. In these glutamine-requiring mutants histidase does not escape from catabolite repression, even when the nitrogen source is growth rate-limiting. Most revertants of the glnB mutant regain the ability to produce glutamine synthetase by a mutation in the glnC site, which is closely linked to the glnA site. In the glnC mutants, glutamine synthetase is produced at a high level, even in media containing an excess of ammonia. In glnC mutants histidase and proline oxidase are not subject to catabolite repression, even in media containing glucose and an excess of ammonia.