Conformal anomaly from gauge fields without gauge fixing
We show how the Weyl anomaly generated by gauge fields, can be computed from manifestly gauge invariant and diffeomorphism invariant exact renormalization group equations, without having to fix the gauge at any stage. Regularisation is provided by covariant higher derivatives and by embedding the Maxwell field into a spontaneously broken $U(1|1)$ supergauge theory. We first provide a realisation that leaves behind two versions of the original $U(1)$ gauge field, and then construct a manifestly $U(1|1)$ supergauge invariant flow equation which leaves behind only the original Maxwell field in the spontaneously broken regime.
Towards a manifestly gauge invariant and universal calculus for Yang-Mills theory
A manifestly gauge invariant exact renormalization group for pure $SU(N)$ Yang-Mills theory is proposed, along with the necessary gauge invariant regularisation which implements the effective cutoff. The latter is naturally incorporated by embedding the theory into a spontaneously broken $SU(N|N)$ super-gauge theory, which guarantees finiteness to all orders in perturbation theory. The effective action, from which one extracts the physics, can be computed whilst manifestly preserving gauge invariance at each and every step. As an example, we give an elegant computation of the one-loop $SU(N)$ Yang-Mills beta function, for the first time at finite $N$ without any gauge fixing or ghosts. It is also completely independent of the details put in by hand, \eg the choice of covariantisation and the cutoff profile, and, therefore, guides us to a procedure for streamlined calculations.
A single amino acid substitution in elongation factor Tu disrupts interaction between the ternary complex and the ribosome
Elongation factor Tu (EF-Tu).GTP has the primary function of promoting the efficient and correct interaction of aminoacyl-tRNA with the ribosome. Very little is known about the elements in EF-Tu involved in this interaction. We describe a mutant form of EF-Tu, isolated in Salmonella typhimurium, that causes a severe defect in the interaction of the ternary complex with the ribosome. The mutation causes the substitution of Val for Gly-280 in domain II of EF-Tu. The in vivo growth and translation phenotypes of strains harboring this mutation are indistinguishable from those of strains in which the same tuf gene is insertionally inactivated. Viable cells are not obtained when the other tuf gene is inactivated, showing that the mutant EF-Tu alone cannot support cell growth. We have confirmed, by partial protein sequencing, that the mutant EF-Tu is present in the cells. In vitro analysis of the natural mixture of wild-type and mutant EF-Tu allows us to identify the major defect of this mutant. Our data shows that the EF-Tu is homogeneous and competent with respect to guanine nucleotide binding and exchange, stimulation of nucleotide exchange by EF-Ts, and ternary complex formation with aminoacyl-tRNA. However various measures of translational efficiency show a significant reduction, which is associated with a defective interaction between the ribosome and the mutant EF-Tu.GTP.aminoacyl-tRNA complex. In addition, the antibiotic kirromycin, which blocks translation by binding EF-Tu on the ribosome, fails to do so with this mutant EF-Tu, although it does form a complex with EF-Tu. Our results suggest that this region of domain II in EF-Tu has an important function and influences the binding of the ternary complex to the codon-programmed ribosome during protein synthesis. Models involving either a direct or an indirect effect of the mutation are discussed.