HslVU in Escherichia coli a new two-component ATP-dependent protease composed of two heatshock proteins, the HslU ATPase and the HslV peptidase which is related to proteasome p-type subunits. Here we show that the reconstituted HslVU enzyme degrades not only certain hydrophobic peptides but also various polypeptides, including insulin B-chain, casein, and carboxymethylated lactalbumin. Maximal proteolytic activity was obtained with a 1 : 2 molar ratio of HslV (a 250-kDa complex) to HslU (a 450-kDa complex). By itself, HslV could slowly hydrolyze these polypeptides, but its activity was stimulated 20-fold by HslU in the presence of ATP. The ATPase activity of HslU was stimulated up to 50% by the protein substrates, but not by nonhydrolyzed proteins, and this stimulation further increased 2-3-fold in the presence of HslV. Concentrations of insulin B-chain that maximally stimulated the ATPase allowed maximal rates of the B-chain hydrolysis. Furthermore, addition of increasing amounts of ADP or N-ethylmaleimide reduced ATP and protein or peptide hydrolysis in parallel. Thus, HslVU is a proteinactivated ATPase as well as an ATP-dependent proteinase, and these processes appear linked. Surprisingly, the protein and peptide substrates do not compete with each other for hydrolysis. Lactacystin strongly inhibits protein degradation, but has little effect on peptide hydrolysis, while the peptide aldehydes are potent inhibitors of hydrolysis of small peptides, but have little effect on proteins. Thus, the functional requirements for ATP-dependent hydrolysis of peptides and proteins appear different.

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The Drosophila eye is a powerful model system to study principles of cell differentiation, proliferation, survival and morphogenesis. However, a high-resolution single cell genomics resource that accurately captures all major cell types of the larval eye disc and their spatiotemporal relationships is lacking. Here, we report transcriptomic and chromatin accessibility data for all known cell types in the developing eye. Photoreceptors appear as streams of cells that represent dynamic developmental timelines. Photoreceptor subtypes are transcriptionally distinct when they begin to differentiate, but then converge upon a common transcriptome just 24 hours later. We identify novel cell type-specific marker genes, enhancers and potential regulators, as well as genes with distinct R3 or R4 photoreceptor specific expression. Finally, we observe that photoreceptor chromatin accessibility is more permissive than non-neuronal lens-secreting cone cells, which show a more restrictive chromatin profile. This single cell genomics atlas will greatly empower the Drosophila eye as a model system.