Regulation of enzyme synthesis in the tryptophan pathway of Acinetobacter calcoaceticus

Abstract

In Acinetobacter calcoaceticus the seven genes coding for the enzymes responsible for tryptophan synthesis map at three chromosomal locations. Two three-gene clusters, one (trpGDC) specifying the small subunit of anthranilate synthase, phosphoribosyl transferase, and indoleglycerol phosphate synthase and the other (trpFBA) specifying phosphoribosyl anthranilate isomerase and both tryptophan synthase subunits, are not linked to each other or to the trpE gene specifying the large anthranilate synthase subunit. When regulation of trp gene expression is studied in the wild type, only the level of the trpF gene product decreases upon addition of tryptophan to the medium. Tryptophan starvation of tryptophan auxotrophs, however, results in increased levels of all the tryptophan enzymes; this and additional evidence suggests that the expression of all the trp genes is subject to repression. The trpGDC genes are coordinately controlled, and the trpE gene is regulated in parallel with them. The trpFBA genes are controlled neither coordinately nor in parallel with the other trp genes, but respond proportionally when compared with each other. So far, two types of constitutive mutants have been found. The first class of mutants apparently occurs in the structural gene for a repressor protein; this repressor locus is unlinked to any of the biosynthetic trp genes and affects only the expression of trpE and the trpGDC cluster. The second class contains mutants closely linked to the trpGDC region; they overproduce only the gene products of this cluster.

Pseudomonas stutzeri and related species undergo natural transformation

“…In some experiments cells were transformed in liquid with purified DNA by procedures based upon those of Cohn and Crawford (7). For the experiment designed to follow the development of transformation competence, cells from a culture of the auxotroph JM302 in the early stationary growth phase were mixed with JM300 DNA in 1 volume of fresh LB medium and incubated for various times to take up the DNA.…”

Gene rearrangements in the evolution of the tryptophan synthetic pathway.

“…The situation in the trpFAB cluster is more complex, however. When wild-type A. calcoaceticus is shifted from minimal medium without tryptophan to tryptophan excess, only the trpF gene responds by a decreased level of expression (39). Apparently trpF is the only trp gene that is not maintained near its maximally repressed level when the cell is growing "normally" and making its own tryptophan.…”

“…Among the tryptophan analog-resistant mutants obtained to date, two types are noteworthy. One has constitutive, derepressed levels for all the enzymes of the pathway (39). It thus resembles trpR mutants in the enteric bacteria and differs from the trpR mutants of P. putida, which affect only the gene cluster for the early enzymes (152).…”

Properties of Acinetobacter calcoaceticus recA and its contribution to intracellular gene conversion

“…For example, intracellular gene conversion can give rise to strains that exhibit substantial genetic instability (Doten et ai, 1987a), and it should be possible to determine if such instability is maintained in organisms lacking a functional recA gene. In addition, rec/4-deficient strains should allow the construction of stable merodiploids and thus facilitate analysis of cytoplasmic interactions between regulatory gene products and their chromosomal targets (Cohn and Crawford, 1976;Haspei et al. 1991;Neidie et ai.…”