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Replicase
Published in Paul Pumpens, Single-Stranded RNA Phages, 2020
Considering that the four subunits of Qβ replicase holoenzyme must be in equivalent molar ratio of the subunits, and that the synthesis of the S1 and EF-Ts in cells is relatively low, Wang (2004) performed coexpression of the phage-specific β-subunit with the other three subunits to determine whether the availability of the host subunits was the contributing factor for the low solubility of the overproduced Qβ replicase when it was expressed alone. Among the different combinations of coexpression experiments, the solubility was found to increase slightly when the β-subunit was coexpressed together with the EF-TuTs. Facing the same problem of the insolubility of the overexpressed β-subunit, Kita et al. (2006) elaborated two procedures to overcome it. First, both EF-Tu and EF-Ts subunits were expressed together with the β subunit, as described above. Second, the β subunit was genetically fused with EF-Tu and EF-Ts and the fused protein, a single-chain α-less Qβ replicase, was found mostly in the soluble fraction and could be readily purified (Kita et al. 2006).
Regulators and Effectors of ras Proteins
Published in Juan Carlos Lacal, Frank McCormick, The ras Superfamily of GTPases, 2017
It has been possible to establish conditions in which exchange factors appear to be limiting. This has been done by introducing into cells (yeast or mammalian) mutant ras proteins such as Asn 17 that are thought to interfere with ras activation.7,21 The evidence that they perform in this way is based on the fact that, in yeast, their toxic properties can be overcome by overexpressing CDC25 and that they interfere much more effectively with normal ras proteins than with oncogenic ras proteins, which are thought to have a reduced requirement for exchange because of their reduced sensitivity to GAP.17 The actual mechanism by which Asn 17 ras-p21 inhibits exchange has not been demonstrated directly, but a working model has been proposed based on the known properties of the bacterial GDP/GTP exchange protein EF-Ts which catalyzes nucleotide exchange on the ras-like protein EF-Tu.2 EF-Ts works by the following mechanism: EF-Ts binds to EF-Tu-GDP.The ternary complex has a reduced affinity for GDP, which now dissociates rapidly (without EF-Ts, the rate of dissociation would be very slow).EF-Tu complexed with EF-Ts now binds GTP; the affinity of the com-plexed form of EF-Tu for GTP is relatively low, but cells contain high concentrations of GTP (up to millimolar, much higher than GDP).EF-Ts dissociates from EF-Tu-GTP, to complete the exchange cycle.
Acne vulgaris: new evidence in pathogenesis and future modalities of treatment
Published in Journal of Dermatological Treatment, 2021
NAI: Bacterial elongation factor Tu (EF-Tu) and EF-Ts are interacting proteins involved in polypeptide chain elongation in protein biosynthesis (52). NAI, a semi-synthetic thiopeptide, is a peptide EF-Tu inhibitor, and highly selective against P. acnes, and is currently under evaluation as a 3% gel for acne (2014-001491-62) (36).