MRX8, the conserved mitochondrial YihA GTPase family member, is required for de novo Cox1 synthesis at suboptimal temperatures in Saccharomyces cerevisiae.

The synthesis of Cox1, the conserved catalytic-core subunit of Complex IV, a multisubunit machinery of the mitochondrial oxidative phosphorylation (OXPHOS) system under environmental stress, has not been sufficiently addressed. In this study, we show that the putative YihA superfamily GTPase, Mrx8, is a bona fide mitochondrial protein required for Cox1 translation initiation and elongation during suboptimal growth condition at 16°C. Mrx8 was found in a complex with mitochondrial ribosomes, consistent with a role in protein synthesis. Cells expressing mutant Mrx8 predicted to be defective in guanine nucleotide binding and hydrolysis were compromised for robust cellular respiration. We show that the requirement of Pet309 and Mss51 for cellular respiration is not bypassed by overexpression of Mrx8 and vice versa. Consistently the ribosomal association of Mss51 is independent of Mrx8. Significantly, we find that GTPBP8, the human orthologue, complements the loss of cellular respiration in Δmrx8 cells and GTPBP8 localizes to the mitochondria in mammalian cells. This strongly suggests a universal role of the MRX8 family of proteins in regulating mitochondrial function.

Pressure dependent ultrasonic characterization of nano-structured w-BN.

The work includes evaluation of elastic constants of wurtzite Boron nitride (w-BN) at different particle-size (5-40 nm) and pressure (0-60 GPa) at 300 K using potential model approach. Size and pressure dependent thermo-physical and ultrasonic parameters are also calculated using evaluated elastic constants. It is found that the elastic constants, ultrasonic velocities and Debye temperature of nanostructured w-BN enhance with increase in pressure and reduction in particle size. The size variation of thermal relaxation time resembles the dependency of thermal conductivity with size. The thermal conductivity of nanostructured w-BN is found to increase with reduction in nanoparticle size.