No abstract

The ubiquitin-like protein BAG-6 protects cells from newly synthesized misfolded proteins by tethering them to the proteasome.

The proteasome activator PA28 binds to both ends of the central catalytic machine, known as the 20 S proteasome, in opposite orientations to form the enzymatically active proteasome. The PA28 family is composed of three members designated ␣, ␤, and ␥; PA28␣ and PA28␤ form the heteropolymer mainly located in the cytoplasm, whereas PA28␥ forms a homopolymer that predominantly occurs in the nucleus. Available evidence indicates that the heteropolymer of PA28␣ and PA28␤ is involved in the processing of intracellular antigens, but the function of PA28␥ remains elusive. To investigate the role of PA28␥ in vivo, we generated mice deficient in the PA28␥ gene. The PA28␥-deficient mice were born without appreciable abnormalities in all tissues examined, but their growth after birth was retarded compared with that of PA28␥ ؉/؊ or PA28␥ ؉/؉ mice. We also investigated the effects of the PA28␥ deficiency using cultured embryonic fibroblasts; cells lacking PA28␥ were larger and displayed a lower saturation density than their wild-type counterparts. Neither the expression of PA28␣/␤ nor the subcellular localization of PA28␣ was affected in PA28␥ ؊/؊ cells. These results indicate that PA28␥ functions as a regulator of cell proliferation and body growth in mice and suggest that neither PA28␣ nor PA28␤ compensates for the PA28␥ deficiency.

Context. We present the results from Suzaku observations of the merging cluster of galaxies CIZA J2242.8+5301 at z = 0.192. Aims. To study the physics of gas heating and particle acceleration in cluster mergers, we investigated the X-ray emission from CIZA J2242.8+5301, which hosts two giant radio relics in the northern and southern part of the cluster. Methods. We analyzed data from three-pointed Suzaku observations of CIZA J2242.8+5301 to derive the temperature distribution in four different directions. Results. The intracluster medium (ICM) temperature shows a remarkable drop from 8.5 +0.8 −0.6 keV to 2.7 +0.7 −0.4 keV across the northern radio relic. The temperature drop is consistent with a Mach number M n = 2.7 +0.7 −0.4 and a shock velocity v shock:n = 2300 +700 −400 km s −1 . We also confirm the temperature drop across the southern radio relic. However, the ICM temperature beyond this relic is much higher than beyond the northern relic, which gives a Mach number M s = 1.7 +0.4 −0.3 and shock velocity v shock:s = 2040 +550 −410 km s −1 . These results agree with other systems showing a relationship between the radio relics and shock fronts which are induced by merging activity. We compare the X-ray derived Mach numbers with the radio derived Mach numbers from the radio spectral index under the assumption of diffusive shock acceleration in the linear test particle regime. For the northern radio relic, the Mach numbers derived from X-ray and radio observations agree with each other. Based on the shock velocities, we estimate that CIZA J2242.8+5301 is observed approximately 0.6 Gyr after core passage. The magnetic field pressure at the northern relic is estimated to be 9% of the thermal pressure.