Reversible unfolding of the β2 subunit of Escherichia coli tryptophan synthetase and its proteolytic fragments

The guanidine hydrochloride-induced reversible unfolding transitions at 4 °C of the β₂ subunit of tryptophan synthetase (l-serine hydrolyase (adding indole) EC. 4.2.1.20) and of its two proteolytic fragments, F₁ and F₂, are compared. The unfolding of the β₂ subunit shows a multistate behaviour, as judged by circular dichroism and fluorescence measurements. When isolated, the two fragments have different stabilities. Within β₂, the region corresponding to the large fragment, F₁ behaves as the corresponding isolated fragment, and no stabilization arising from the interaction with the complementary fragment can be detected. The same behaviour is suggested for the small fragment, F₂. These results lead to the apparent conclusion that, at least under these experimental conditions, the interactions between domains do not contribute greatly to the energetics of the folding process of the large β₂ protein.     

Restriction in vivo

Summary Degradation products of restricted T4 DNA induced filamentation, mutagenesis, and to a lesser extent, synthesis of recA protein in wild type cells but not in recA, lexA or recBC mutants of Escherichia coli. We conclude that the structural damage to the DNA caused by restriction cleavage and exonuclease V degradation can induce SOS functions. Degradation of restricted nonglucosylated T4 DNA by exonuclease V delayed cell division and induced filament formation and mutagenesis in lexA ⁺ but not in lexA ^- cells. Delay of cell division was also dependent upon recA and recBC funtions. Such degradation of DNA also dramatically increased mutagenesis in tif ^- Sfi^- cells at 42°C. The synthesis of recA protein continued in the restricting host after infection by the nonglucosylated T4 phage, but enhanced synthesis is not induced to the extent seen in SOS induced tif ^- cells grown at 42°. We also found that restriction of nonglucosylated T4 was alleviated in UV irradiated cells. The UV induced alleviation of rgl and r _K restriction depended upon post irradiation protein synthesis and was not observed in recA, lexA or recBC mutants.     

Optimization of a medium for a high yield production of spore-crystal preparation ofBacillus thuringiensis effective against the Egyptian cotton leaf wormSpodoptera littoralis Boisd.

Summary The continuous culture (chemostat) technique was used for the optimization of a medium which supported the production of a high yield spore-crystal preparation ofBacillus thuringiensis (isolate Bt 24) (a maximum of 4 × 10⁹spores/ml) on a pilot-scale. The preparation demonstrated a high insecticidal activity against second-instar larvae ofSpodoptera littoralis Boisd.     

Cloned genes for bacteriophage T4 late functions are expressed in Escherichia coli

We have constructed derivatives of plasmid pMB9 carrying EcoRI digestion fragments of bacteriophage T4 DNA that code for late gene functions. When Escherichia coli strains carrying these plasmids are infected with T4 amber mutants, burst sizes up to 30% of the wild-type level are obtained. Single burst experiments imply that the phage progeny result from complementation and do not depend on marker rescue. By electrophoretic and immunological techniques, we have established that the cloned T4 late genes are transcribed and translated in uninfected cells. A serum blocking assay has been used to quantitate the levels of one of the T4 gene products, gp11, before and after T4 infection. Uninfected cells containing the cloned T4 gene 11 DNA have 0.1% and mini cells have 1% of the gp11 levels per unit protein found in cells late after T4 wild-type infection. There is little or no additional gp10 and gp11 formed from the cloned genes after T4 infection.     

Formation of Short-Chain Fatty Acids from H(2) and CO(2) by a Mixed Culture of Bacteria

The biological utilization of CO(2) and H(2) for the formation of short-chain fatty acids was studied by using a mixed culture of bacteria. Optimization of a medium was carried out in continuous culture to identify limiting factors which controlled growth and production of organic acids. The optimal pH for growth and acid production was 7.0 at 37 degrees C; the maximal cell concentration obtained was 5.9 g of cells per liter (dry weight), and the maximal amount of volatile acids formed was 4.7 g/liter, with acetic acid as the predominant acid. With the optimized medium, it was found that the rate of transfer of hydrogen or carbon dioxide, or both, from gas to liquid was the limiting factor which controlled growth and production of acids.     

The apparent stimulation of proteolysis by adenosine triphosphate in tissue homogenates (Short Communication)

Reports that ATP promotes proteolysis in tissue homogenates were reinvestigated. Although ATP increased production of material reacting with ninhydrin or Folin-phenol reagent, ATP did not stimulate protein degradation in such extracts. AMP and adenosine acted similarly to ATP. Deamination of the added nucleotides to produce ammonia caused the increase in ninhydrin-positive material.     

A protein produced by male strains of Escherichia coli K-12 which increases the yield of recombinants in conjugation: its nature and mode of action

Summary A protein present in filtrates of E. coli K-12 male strains is responsible for their ability to increase the yield of recombinants in conjugation and to inhibit nitrogen mustard after-effect (NMAE) in F ^- cells. The protein, designated recombination-stimulating factor (RSF), was purified 200–300 times from HfrC filtrate. Two Rsf^- mutants of strain HfrC were isolated which fail to produce RSF; these mutations affect an episomal gene. RSF action involves the attachment of RSF to the F ^- cell surface and requires the integrity of the RSF-cell complex. Some step of recombination after the transfer of the donor chromosomal fragment into the recipient is affected by RSF.