The proper regulation of factors involved in mitosis is crucial to ensure normal cell division. Levels and activities of proteins are regulated in many ways, one of which is ubiquitin-mediated protein degradation. E3 ubiquitin ligases are involved in targeting specific substrates for degradation by facilitating their ubiquitination. In seeking to elucidate additional biological roles for Cul3 we performed a two-hybrid screen and identified Ctb9/ KLHDC5 as a Cul3-interacting protein. Overexpression of Ctb9/KLHDC5 resulted in an increase in microtubule density as well as persistent microtubule bridges between post-mitotic cells. Conversely, down-regulation of Ctb9/KLHDC5 showed a pronounced reduction in microtubule density. Based on these observations, we examined the interactions between Cul3, Ctb9/KLHDC5, and the microtubule-severing protein, p60/katanin. Here we show that p60/katanin interacts with a complex consisting of Cul3 and Ctb9/KLHDC5, which results in ubiquitin laddering of p60/katanin. Also, Cul3-deficient cells or Ctb9/KLHDC5-deficient cells show an increase in p60/katanin levels, indicating that Cul3/Ctb9/KLHDC5 is required for efficient p60/katanin removal. We demonstrate a novel regulatory mechanism for p60/katanin that occurs at the level of targeted proteolysis to allow normal mitotic progression in mammalian cells.Due to the irreversible nature of protein degradation, ubiquitin-mediated proteolysis is an effective method to sequentially order cell cycle events. During ubiquitin-mediated protein degradation, the E1 5 ubiquitin-activating enzyme forms an ATP-dependent thioester bond with a ubiquitin molecule. The activated ubiquitin is subsequently transferred to an E2 ubiquitin-conjugating enzyme, which can either directly attach ubiquitin onto its substrate or act in concert with an E3 ubiquitin ligase to achieve the same end (1, 2). The E3 serves a dual function in recruiting the E2 ubiquitin-conjugating enzyme to the substrate and in positioning the two in close proximity.
Amidst the COVID‐19 pandemic, many colleges shifted to online learning, creating a need for teaching materials that could be deployed in the online setting. A pair of virtual laboratory exercises with a COVID‐19 theme were created for first year Biology majors to introduce students to the topics of polymerase chain reaction and gel electrophoresis. The exercises were effective in promoting student learning of both topics in an online asynchronous setting, and could easily be adapted for use in other courses or in a synchronous online setting.
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