Ubiquiton-An inducible, linkage-specific polyubiquitylation tool.

The posttranslational modifier ubiquitin regulates most cellular processes. Its ability to form polymeric chains of distinct linkages is key to its diverse functionality. Yet, we still lack the experimental tools to induce linkage-specific polyubiquitylation of a protein of interest in cells. Here, we introduce a set of engineered ubiquitin protein ligases and matching ubiquitin acceptor tags for the rapid, inducible linear (M1-), K48-, or K63-linked polyubiquitylation of proteins in yeast and mammalian cells. By applying the so-called "Ubiquiton" system to proteasomal targeting and the endocytic pathway, we validate this tool for soluble cytoplasmic and nuclear as well as chromatin-associated and integral membrane proteins and demonstrate how it can be used to control the localization and stability of its targets. We expect that the Ubiquiton system will serve as a versatile, broadly applicable research tool to explore the signaling functions of polyubiquitin chains in many biological contexts.

Linkage reprogramming by tailor-made E3s reveals polyubiquitin chain requirements in DNA-damage bypass.

A polyubiquitin chain can adopt a variety of shapes, depending on how the ubiquitin monomers are joined. However, the relevance of linkage for the signaling functions of polyubiquitin chains is often poorly understood because of our inability to control or manipulate this parameter in vivo. Here, we present a strategy for reprogramming polyubiquitin chain linkage by means of tailor-made, linkage- and substrate-selective ubiquitin ligases. Using the polyubiquitylation of the budding yeast replication factor PCNA in response to DNA damage as a model case, we show that altering the features of a polyubiquitin chain in vivo can change the fate of the modified substrate. We also provide evidence for redundancy between distinct but structurally similar linkages, and we demonstrate by proof-of-principle experiments that the method can be generalized to targets beyond PCNA. Our study illustrates a promising approach toward the in vivo analysis of polyubiquitin signaling.

Efficacy of minute virus of mice (MVM) inactivation utilizing high temperature short time (HTST) pasteurization and suitability assessment of pasteurized, concentrated glucose feeds in Chinese hamster ovary (CHO) cell expression systems.

There is a growing need to provide effective adventitious agent mitigation for high risk upstream cell culture raw materials used for the production of biologics. It is also highly important in the growing fields of cell and gene therapies. Glucose is a critical raw material necessary for effective cell growth and productivity; however, glucose is the highest risk animal-origin-free raw material for viral contamination, and often the highest risk raw material in the upstream process as more companies move to chemically defined media. This study examines the efficacy of utilizing High Temperature Short Time (HTST) pasteurization for inactivation of physiochemically resistant, worst-case parvovirus using a bench-scale HTST system. We demonstrated approximately six log inactivation of Minute Virus of Mice (MVM) in concentrated glucose feeds without impacting the subsequent performance of the glucose in a Chinese Hamster Ovary (CHO) expression system.