Characterization of Pseudomonas aeruginosa mutants deficient in the establishment of lysogeny.

Mutants of Pseudomonas aeruginosa with impaired ability to establish a lysogenic relationship with temperate bacteriophage (Les-) have been isolated. These les mutations map to two areas of the P. aeruginosa chromosomal map as determined by conjugational and transductional analyses. Two phenotypic classes of Les- mutants were identified. One class of mutations has pleiotropic effects on DNA metabolism. These mutants are unable to recombine genetic material acquired as a result of either conjugation or transduction (Rec-). In addition, the ability of these Les- Rec- mutants to repair UV-induced damage to bacteriophage is reduced (host-cell reactivation deficient, Hcr-). Mutants of the second class are Les-, Rec+, and Hcr+.     

Salmonella typhimurium mutants affecting establishment of lysogeny

Summary Salmonella typhimurium mutants have been isolated in which phage P22 fails to establish lysogeny. These appear to be defective in cAMP metabolism. A phage mutation overcoming the bacterial defect has been mapped between gene c ₁ and gene 12.     

Threonine production by regulatory mutants of Serratia marcescens.

beta-Hydroxynorvaline (alpha-amino-beta-hydroxyvaleric acid)-resistant mutants of Serratia marcescens deficient in both threonine dehydrogenase and threonine deaminase were isolated and characterized. One of the mutants, strain HNr21, lacked feedback inhibition of threonine-sensitive aspartokinase and homoserine dehydrogenase, was repressed for the two enzymes, and produced 11 mg of threonine per ml of medium containing a limiting amount of isoleucine. The other mutant, strain HNr59, was constitutively derepressed for aspartokinase and homoserine dehydrogenase. Its kinase was sensitive to feedback inhibition, but its dehydrogenase was insensitive to feedback inhibition. This strain produced 5 mg of threonine per ml of medium containing either a limiting or an excess amount of isoleucine. Diaminopimelate auxotrophs derived from strain HNr59 produced more threonine (13 mg/ml) than the parent strain. However, similar auxotrophs derived from strain HNr21 produced the same amount of threonine as that produced by the parent strain.     

Threonine production by regulatory mutants of Serratia marcescens.

beta-Hydroxynorvaline (alpha-amino-beta-hydroxyvaleric acid)-resistant mutants of Serratia marcescens deficient in both threonine dehydrogenase and threonine deaminase were isolated and characterized. One of the mutants, strain HNr21, lacked feedback inhibition of threonine-sensitive aspartokinase and homoserine dehydrogenase, was repressed for the two enzymes, and produced 11 mg of threonine per ml of medium containing a limiting amount of isoleucine. The other mutant, strain HNr59, was constitutively derepressed for aspartokinase and homoserine dehydrogenase. Its kinase was sensitive to feedback inhibition, but its dehydrogenase was insensitive to feedback inhibition. This strain produced 5 mg of threonine per ml of medium containing either a limiting or an excess amount of isoleucine. Diaminopimelate auxotrophs derived from strain HNr59 produced more threonine (13 mg/ml) than the parent strain. However, similar auxotrophs derived from strain HNr21 produced the same amount of threonine as that produced by the parent strain.     

Chloramphenicol resistant mutants of Bacillus subtilis

Summary Telve chloramphenicol resistant (CM ^r)-mutants were isolated from B. subtilis ATCC 6633 and were classified into the following six groups. Group I. No 50s ribosomal protein change was detectable. Ribosomes did not show alteration of the binding ability to CM or to erythromycin in vitro. Group II. A 50s protein, 50a, was altered. Ribosomes did not show alteration of the binding ability to CM or to erythromycin in vitro. The genes specifying the 50a protein was in the cysA-str region on B. subtilis chromosome. Group III. A 50s protein, 50b, was altered. Biological properties of the ribosomes were the same as Group I or II so fas as examined. The genes for 50b protein was in the cysA-str region. Group IV. A 50s protein, 50c, was altered. Ribosomes showed a definite decrease in ability to bind to CM in vitro. The binding of erythromycin to the ribosomes was not impaired. The chromosomal locus of the CM ^r (and for 50c protein) was in the cysA-str region. Group V. A 50s protein, 50e, was changed. The ability of the ribosomes to bind in vitro both to CM and to erythromycin was greatly reduced. The genetic locus of the CM ^r (and for 50e protein) was in the cysA-str region. Group VI. A 50s protein, 50f, was altered. Ribosomes showed a decrease in ability to bind in vitro both to CM and to erythromycin. The genes for 50f protein was in the cysA-str region.The results suggest that the ribosomal resistance to CM may be caused by an independent change of at least several 50s ribosomal protein species. The genetic data shown here and those reported previously show that at least two 30s and seven 50s ribosomal protein genes are situated in the cysA-str region on B. subtilis chromosome.     

Multiple effects of Fis on integration and the control of lysogeny in phage lambda.

Fis is a small, basic, site-specific DNA-binding protein present in Escherichia coli. A Fis-binding site (F) has been previously identified in the attP recombination site of phage lambda (J. F. Thompson, L. Moitoso de Vargas, C. Koch, R. Kahmann, and A. Landy, Cell 50:901-908, 1987). The present study demonstrates that in the absence of the phage-encoded Xis protein, the binding of Fis to F can stimulate integrative recombination and therefore increase the frequency of lambda lysogeny in vivo. Additionally, Fis exerts a stimulatory effect on both integration and lysogeny that is independent of binding to the attP F site. Maintenance of the lysogenic state also appears to be enhanced in the presence of Fis, as shown by the increased sensitivity of lambda prophages encoding temperature-sensitive repressors to partial thermoinduction in a fis mutant. In the presence of Xis, however, Fis binding to F interferes with integration by stimulating excision, the competing back-reaction. Since Fis stimulates both excision and integration, depending on the presence or absence of Xis, respectively, we conclude that Xis binding to X1 is the key determinant directing the formation of an excisive complex.     

Deletion mutants of bacteriophage lambda

Summary The high frequency of recombination which results from site-specific recombination acting on certain attachment site configurations leads to unlinkage of the genes on either side of att.     

Studies on lambda virulent mutants

Summary Lambda virC mutant, presumably an operator mutant for the operon including x, y, CII and O genes (Fig. 1), produce clearish plaque on a sensitive bacteria.Four revertants producing turbid plaques were isolated from virC and the mutational sites of which were studied. One (tw ₁) is located very close to and on the left side of virC₃₄, and another (tw ₃₂) is at the almost same site of virC₃₄. The others (tx ₆ and tx ₅₃) are located on the right side of virC₃₄. tx recombinants have been isolated and characterized. These recombinants produce very turbid plaques and the rate of the repressor formation in the presence of CIts repressor is somewhat higher than that of wild type. tx develops very poorly after infection to sensitive cells but CItx develops normally. tx lysogens synthesize two to three times more exonuclease than the wild type lysogen. On a function of x region for the repressor formation and on a presence of a possible anti-repressor were discussed. The mutant tw ₁ might be a promotor mutation of the CI-rex operon.This material has been published as an abstract in Jap. J. Genetics 45, 474 (1970).