Baldauf S L, Cardani M A, Bender R A
Department of Biology, University of Michigan, Ann Arbor 48109.
J Bacteriol. 1988 Dec;170(12):5588-93. doi: 10.1128/jb.170.12.5588-5593.1988.
Galactose appears to be the physiological inducer of the chromosomal lac operon in Klebsiella aerogenes. Both lactose and galactose are poor inducers in strains having a functional galactose catabolism (gal) operon, but both are excellent inducers in gal mutants. Thus the slow growth of K. aerogenes on lactose reflects the rapid degradation of the inducer. Several pts mutations were characterized and shown to affect both inducer exclusion and permanent catabolite repression. The beta-galactosidase of pts mutants cannot be induced at all by lactose, and pts mutants appear to have a permanent and constitutive inducer exclusion phenotype. In addition, pts mutants show a reduced rate of glucose metabolism, leading to slower growth on glucose and a reduced degree of glucose-mediated permanent catabolite repression. The crr-type pseudorevertants of pts mutations relieve the constitutive inducer exclusion for lac but do not restore the full level of glucose-mediated permanent catabolite repression and only slightly weaken the glucose-mediated inducer exclusion. Except for weakening the glucose-mediated permanent catabolite repression, pts and crr mutations have no effect on expression of the histidine utilization (hut) operons.
半乳糖似乎是产气克雷伯菌中染色体乳糖操纵子的生理诱导物。在具有功能性半乳糖分解代谢（gal）操纵子的菌株中，乳糖和半乳糖都是较弱的诱导物，但在gal突变体中二者都是优良的诱导物。因此，产气克雷伯菌在乳糖上生长缓慢反映了诱导物的快速降解。对几个pts突变进行了表征，结果表明它们既影响诱导物排除又影响永久性分解代谢物阻遏。pts突变体的β-半乳糖苷酶根本不能被乳糖诱导，并且pts突变体似乎具有永久性的组成型诱导物排除表型。此外，pts突变体显示出葡萄糖代谢速率降低，导致在葡萄糖上生长较慢以及葡萄糖介导的永久性分解代谢物阻遏程度降低。pts突变的crr型假回复突变解除了对lac的组成型诱导物排除，但没有恢复葡萄糖介导的永久性分解代谢物阻遏的完全水平，只是略微减弱了葡萄糖介导的诱导物排除。除了减弱葡萄糖介导的永久性分解代谢物阻遏外，pts和crr突变对组氨酸利用（hut）操纵子的表达没有影响。
