Understanding buffering mechanisms for various perturbations is essential for understanding robustness in cellular systems. Protein-level dosage compensation, which arises when changes in gene copy number do not translate linearly into protein level, is one mechanism for buffering against genetic perturbations. Here, we present an approach to identify genes with dosage compensation by increasing the copy number of individual genes using the genetic tug-of-war technique. Our screen of chromosome I suggests that dosage-compensated genes constitute approximately 10% of the genome and consist predominantly of subunits of multi-protein complexes. Importantly, because subunit levels are regulated in a stoichiometry-dependent manner, dosage compensation plays a crucial role in maintaining subunit stoichiometries. Indeed, we observed changes in the levels of a complex when its subunit stoichiometries were perturbed. We further analyzed compensation mechanisms using a proteasome-defective mutant as well as ribosome profiling, which provided strong evidence for compensation by ubiquitin-dependent degradation but not reduced translational efficiency. Thus, our study provides a systematic understanding of dosage compensation and highlights that this post-translational regulation is a critical aspect of robustness in cellular systems.

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The reliability of electrostatically actuated ohmic contact type MEMS relays has been investigated. Multi-contact MEMS relays laterally actuated using electrostatic comb-drive actuators were used in this study. The MEMS relays were fabricated using the MetalMUMPs process, which uses a 20 µm thick electroplated nickel as the structural layer. A 3 µm thick gold layer was electroplated on the electrical contact surfaces. An example MEMS relay with planar contacts of area 80 µm × 20 µm and spacing of 10 µm between the movable and fixed contacting surfaces is discussed. The overall size of the relay is approximately 3 mm × 3 mm. ‘Resistance versus applied voltage’ characteristics have been studied. At an applied dc bias voltage of 120 V, the movable fingers make initial contact with the fixed fingers. The ‘resistance versus applied voltage’ characteristics have been measured for an applied bias voltage in the range of 172–220 V. Reliability testing of the MEMS relay up to one million actuations has been carried out and the resistance degradation with actuation cycles is discussed.

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