The budding yeast, Saccharomyces cerevisiae, has three cullin proteins, which act as platforms for Cullin-based E3 ubiquitin ligases. Genetic evidence indicates that Cul8, together with Mms1, Mms22, and Esc4, is involved in the repair of DNA damage that can occur during DNA replication. Cul8 is thought to form a complex with these proteins, but the composition and the function of Cul8-based E3 ubiquitin ligases remain largely uncharacterized. Herein, we report a comprehensive biochemical analysis of Cul8 complexes. Cul8 was found to form a Cul8-Mms1-Mms22-Esc4 complex under physiological conditions, with Mms1 bridging Cul8 and Mms22 and Mms22 bridging Mms1 and Esc4. Domain analysis demonstrated that the N-terminal region of Mms1 and the C-terminal region of Mms22 are required for the Mms1-Mms22 interaction, whereas the N-terminal region of Mms22 is required for the Mms22-Esc4 interaction. We also found other Cul8-Mms1-binding proteins Ctf4, Esc2, and Orc5 using yeast two-hybrid screening. Esc4 and Ctf4 bound to Mms22 directly and bound to Cul8-Mms1 in the presence of Mms22, whereas Esc2 and Orc5 interacted with both Cul8 and Mms1, independently. We found that Cul8, Mms1, and Mms22 participated in the regulation of transcriptional silencing of yeast telomeres. These results suggest that Cul8-Mms1, as part of various protein complexes, is involved in the regulation of chromatin metabolism.The ubiquitin/proteasome-dependent protein degradation system is a highly regulated and specific system for targeted protein degradation and is involved in virtually all of the biological processes in eukaryotes. In this system, the ubiquitin is conjugated to a substrate protein, and subsequent polyubiquitination of the substrate ultimately creates a recognition site for the 26 S proteasome. The specificity of protein degradation is determined by the recognition of specific substrates at specific times.Protein ubiquitination involves three enzymes: E1, 3 E2, and the ubiquitin ligase E3. Only E3 ligases can directly recognize specific substrates, i.e. they determine substrate specificity. There are many different types of E3 ligases. One such E3 is the cullin-based ubiquitin ligase. The Skp1-cullin-F-box protein (SCF) complex is the most studied cullin-based E3 ubiquitin ligase (1, 2). SCF consists of the RING finger protein, Rbx1, cullin, Cul1/Cdc53, the adapter protein, Skp1, and a substrate recognition subunit, which is an F-box protein. Rbx1, Cul1, and Skp1 are constitutive subunits of SCF, but the F-box protein is a variable subunit; multiple F-box proteins are present in cells and respond to different substrates.Multiple and different cullins are found in different species, e.g. humans have six cullins, namely Cul1 through Cul5 and Cul7. Each cullin has specific adapter proteins and substrate recognition substrates, such as Elongin BC and Cul2-box proteins for Cul2, BTB (Bric-a-brac, Tramtrack, Broad complex) proteins for Cul3, Ddb1 and Cul4-box proteins for Cul4, Elongin BC and SOCS box proteins for Cul5, and Skp1 and F-box...

Clethra barbinervis Sieb. et Zucc. accumulates Nickel (Ni) and Cobalt (Co) at high concentrations., We hypothesized that C. barbinervis cannot distinguish between Ni and Co because of the similar chemical properties of these two elements. To confirm this hypothesis and understand the role of these elements in C. barbinervis, we conducted a hydroponic split-root experiment using Ni and Co solutions. We found that the bioconcentration factor (BCF; metal concentration of each tissue/metal concentrations of each treatment solution) of Ni and Co did not significantly differ in the roots, but the BCF for Co was higher than that for Ni in the leaves. The leaves of C. barbinervis accumulated Ni or Co at high concentrations. We also found the simultaneous accumulation of Ni and Co by the multiple heavy metal treatments (Ni and Co) at high concentrations similar to those for the single treatments (Ni or Co). Elevated sulfur concentrations occurred in the roots and leaves of Co-treated seedlings but not in Ni. This result indicates that S was related to Co accumulation in the leaves. These results suggest that C. barbinervis distinguishes between Ni and Co during transport and accumulation in the leaves but not during root uptake.

No abstract

No abstract

No abstract