A direct proofreader–clamp interaction stabilizes the Pol III replicase in the polymerization mode

Processive DNA synthesis by the αεθ core of the Escherichia coli Pol III replicase requires it to be bound to the β₂ clamp via a site in the α polymerase subunit. How the ε proofreading exonuclease subunit influences DNA synthesis by α was not previously understood. In this work, bulk assays of DNA replication were used to uncover a non‐proofreading activity of ε. Combination of mutagenesis with biophysical studies and single‐molecule leading‐strand replication assays traced this activity to a novel β‐binding site in ε that, in conjunction with the site in α, maintains a closed state of the αεθ–β₂ replicase in the polymerization mode of DNA synthesis. The ε–β interaction, selected during evolution to be weak and thus suited for transient disruption to enable access of alternate polymerases and other clamp binding proteins, therefore makes an important contribution to the network of protein–protein interactions that finely tune stability of the replicase on the DNA template in its various conformational states.     

Chemostat optimization of biomass production of a mixed bacterial culture utilizing methanol

Summary A continuous culture technique was used to optimize the medium composition and growth conditions of a mixed bacterial culture utilizing methanol. The improved medium resulted in satisfactory growth, high-yield coefficients and gave a product containing reduced polysaccharide concentrations. Optimal growth and biomass yields occurred at pH 6.8 a temperature of 37° C and dissolved oxygen at >20% saturation. The maximum growth rate was 0.58 h^–1 and maximum biomass yield 0.48 g g^–1. The protein content of the product ranged between 81%–83%, and nucleic acid content between 10%–12%, increasing with growth rate. The amino acid profile of the mixed culture product met and, in some cases, exceeded the UN Food and Agricultural Organization standard, indicating a good source of feed protein.Offprint requests to: A. S. Abu-Ruwaida     

Yield depression in methanol-utilizing batch cultures

Summary Yield depression, as opposed to growth inhibition, in batch cultures of methanol-utilizing microorganisms is discussed. Under conditions where the yield coefficient varies, the effect on oxygen demand has been predicted for exponentionally growing cultures.     

Reduction of nucleic acid content in cell biomass of methanol-utilizing mixed bacterial culture by heat treatment

Summary A heat treatment method to reduce nucleic acid content in cell biomass of a mixed methanol-utilizing bacterial culture was studied. Maximum nucleic acid reduction in the bacterial cells was achieved by using heat shock at 65°C for 5–10 min followed by 2 h incubation at 55°C and 7.2±0.2 pH. In this treatment, 81–85% nucleic acid content was removed from the cells without affecting their true protein content and essential amino acids profile.     

Role of calcineurin biosignaling in cell secretion and the possible regulatory mechanisms

Cyclic adenosine monophosphate (cAMP) and calcium ions (Ca²⁺) are two chemical molecules that play a central role in the stimulus-dependent secretion processes within cells. Ca²⁺ acts as the basal signaling molecule responsible to initiate cell secretion. cAMP primarily acts as an intracellular second messenger in a myriad of cellular processes by activating cAMP-dependent protein kinases through association with such kinases in order to mediate post-translational phosphorylation of those protein targets. Put succinctly, both Ca²⁺ and cAMP act by associating or activating other proteins to ensure successful secretion. Calcineurin is one such protein regulated by Ca²⁺; its action depends on the intracellular levels of Ca²⁺. Being a phosphatase, calcineurin dephosphorylate and other proteins, as is the case with most other phosphatases, such as protein phosphatase 2A (PP2A), PP2C, and protein phosphatase-1 (PP1), will likely be activated by phosphorylation. Via this process, calcineurin is able to affect different intracellular signaling with clinical importance, some of which has been the basis for development of different calcineurin inhibitors. In this review, the cAMP-dependent calcineurin bio-signaling, protein-protein interactions and their physiological implications as well as regulatory signaling within the context of cellular secretion are explored.