The 26S proteasome is a highly conserved multisubunit protease that degrades ubiquitinated proteins in eukaryotic cells. The 26S proteasome consists of the proteolytic core particle (CP) and one or two 19S regulatory particles (RPs). Although the mechanisms of CP assembly are well described, the mechanism of RP assembly is largely unknown. Here, we show that four proteasome-interacting proteins (PIPs), Nas2/p27, Nas6/gankyrin, Rpn14/PAAF1, and Hsm3/S5b, bind specific Rpt subunits of the RP and interact each other genetically. Lack of these PIPs resulted in defective assembly of the 26S proteasome at an early stage, suggesting that these proteins are bona fide RP chaperones. Each of the RP chaperones formed distinct specific subassemblies of the base components and escorted them to mature RPs. Our results indicate that the RP assembly is a highly organized and elaborate process orchestrated by multiple proteasome-dedicated chaperones.

No abstract

The partition coefficient, K, of w-phenylalkanols (C6HS(CH2)90H, mp = 0-6) between the bulk water and micelles of sodium dodecyl sulfate (SDS) was determined at 25 O C by a differential spectroscopic method. A new approach for the determination of K has been proposed, taking both the effect of added alkanol on the concentration of monomerically dissolved surfactant in micellar solutions and the fraction of the amount of solubiiized alkanol in that of added alkanol into account, K is found to be independent of the concentration of SDS from just above the critical micelle concentration to high concentration, as well as the concentration of added alkanols. The linear dependence of the free energy change on the alkyl chain length of the alkanols (mP 2 3) on solubilization in micelles calculated from K makes it clear that the contribution of a methylene group to the free energy change is -2.40 k J mol-' in accord with the corresponding value for I-alkanols and that the hydrophobicity of the phenyl group corresponds to that of 3.5 methylene groups. The interaction of the phenylalkanols with SDS has also been discussed. (9) Treiner, C.; Chattopadhyay, A. K.; Bury, R. J. Colloid Interfuce Sci. 1985, 104, 569.

No abstract

Single-rooted soybean leaves were used to investigate the suppression of photosynthesis through end-product inhibition during acclimation to CO(2 )enrichment. The photosynthetic activity was greater in leaves cultured at a CO(2) partial pressure of 70 Pa (high-CO(2)) than that in the leaves cultured at 35 Pa CO(2) (control) during the initial exposure to CO(2) enrichment but then decreased rapidly with a large accumulation of starch, to well below the level of the control leaves. The response curve of photosynthesis (A) to the intercellular CO(2) concentration (Ci) in the high-CO(2) leaves cultured long-term exhibited a significantly low initial gradient. However, on exposure to darkness for 48 h, the initial gradient of the A to Ci curve and rate of photosynthesis were completely restored, and almost all of the accumulated starch was expended. The ribulose bisphosphate carboxylase (RuBPcase) content and activation ratio in the high-CO(2) leaves remained high and roughly constant during the experiment, and were unchanged by the exposure, while this enzyme was slightly inactivated or inhibited after long-term exposure to CO(2) enrichment. The lower rate of photosynthesis in the high-CO(2) leaves could be linearly increased to a rate approaching the control level by increasing the external atmospheric [CO(2)], which thereby compensated for a reduced CO(2) transfer diffusion from the intercellular space to the stroma in chloroplasts. It is consequently concluded that, during the acclimation to CO(2 )enrichment, the suppression of photosynthesis through end-product inhibition was mainly caused by a lowering of the carboxylation efficiency of RuBPcase due to hindrance of CO(2) diffusion from the intercellular space to the stroma in chloroplasts brought about by the large accumulation of starch.