Autophagy is the mechanism by which cytoplasmic components and organelles are degraded by the lysosomal machinery in response to diverse stimuli including nutrient deprivation, intracellular pathogens, and multiple forms of cellular stress. Here, we show that the membrane-associated E3 ligase RNF5 regulates basal levels of autophagy by controlling the stability of a select pool of the cysteine protease ATG4B. RNF5 controls the membranal fraction of ATG4B and limits LC3 (ATG8) processing, which is required for phagophore and autophagosome formation. The association of ATG4B with—and regulation of its ubiquitination and stability by—RNF5 is seen primarily under normal growth conditions. Processing of LC3 forms, appearance of LC3-positive puncta, and p62 expression are higher in RNF5−/− MEF. RNF5 mutant, which retains its E3 ligase activity but does not associate with ATG4B, no longer affects LC3 puncta. Further, increased puncta seen in RNF5−/− using WT but not LC3 mutant, which bypasses ATG4B processing, substantiates the role of RNF5 in early phases of LC3 processing and autophagy. Similarly, RNF-5 inactivation in Caenorhabditis elegans increases the level of LGG-1/LC3::GFP puncta. RNF5−/− mice are more resistant to group A Streptococcus infection, associated with increased autophagosomes and more efficient bacterial clearance by RNF5−/− macrophages. Collectively, the RNF5-mediated control of membranalATG4B reveals a novel layer in the regulation of LC3 processing and autophagy.

Lipid droplets (LDs) are dynamic cellular organelles responsible for the storage of neutral lipids, and are associated with a multitude of metabolic syndromes. Here we report monodansylpentane (MDH) as a high contrast blue-fluorescent marker for LDs. The unique spectral properties make MDH easily combinable with other green and red fluorescent reporters for multicolor fluorescence imaging. MDH staining does not apparently affect LD trafficking, and the dye is extraordinarily photo-stable. Taken together MDH represents a reliable tool to use for the investigation of dynamic LD regulation within living cells using fluorescence microscopy.

Dual-slope converters use time to perform analog-to-digital conversion but require 2 N +1 clock cycles to achieve N bits of precision. We describe a novel algorithm that also uses time to perform analog-to-digital conversion but requires 5N clock cycles to achieve N bits of precision via a successive sub-ranging technique. The algorithm requires one asynchronous comparator, two capacitors, one current source, and a state machine. Amplification of two is achieved without the use of an explicit amplifier by simply doing things twice in time. The use of alternating Voltage-to-Time and Timeto-Voltage conversions provides natural error cancellation of comparator offset and delay, 1/f noise, and switching charge-injection. The use of few components and an efficient mechanism for amplification and error cancellation allow for energy-efficient operation: In a 0.35 µm implementation, we were able to achieve 12 bits of DNL limited precision or 11 bits of thermal noise-limited precision at a sampling frequency of 31.25kHz with 75µW of total analog and digital power consumption. These numbers yield a thermal noise-limited energy-efficiency of 1.17pJ per quantization level making it one of the most energy-efficient converters to date in the 10 to 12 bit precision range. This converter could be useful in low-power hearing aids after analog gain control has been performed on a microphone front-end. An 8 bit audio version of our converter in a 0.18µm process consumes 960nW and yields an energy-efficiency of 0.12pJ per quantization level, perhaps the lowest ever reported. This converter may be useful in biomedical and sensor-network applications where energy-efficiency is paramount. Our algorithm has inherent advantages in time-to-digital conversion. It can be generalized to easily digitize power-law functions of its input, and it can be used in an interleaved architecture if higher speed is desired.

We report a firm evidence of luminescence from InN clusters in InGaN/GaN multiple quantum wells. Photoluminescence, photoluminescence excitation, and Raman scattering measurements have been employed to study the optical properties of InGaN/GaN multiple quantum wells. A careful examination of the low energy shoulders of the main peak luminescence reveals the fact that their separation is in good agreement with the longitudinal optical phonon energy of pure InN film measured by Raman scattering. A large Stokes-like shift between the emission peak energy and the absorption edge is found; it increases with increasing indium content. All these observations can be explained in a consistent way by the effect of localization due to self-organized InN clusters within InGaN layers. Our results thus strongly suggest that the emission mechanism of InGaN/GaN quantum wells originates from radiation recombination within the localized states of self-organized InN clusters.