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The accuracy of crucial nuclear processes such as transcription, replication, and repair, depends on the local composition of chromatin and the regulatory proteins that reside there. Understanding these DNA-protein interactions at the level of specific genomic loci has remained challenging due to technical limitations. Here, we introduce a method termed "DNA O-MAP", which uses programmable peroxidase-conjugated oligonucleotide probes to biotinylate nearby proteins. We show that DNA O-MAP can be coupled with sample multiplexed quantitative proteomics and next-generation sequencing to quantify DNA-protein and DNA-DNA interactions at specific genomic loci., Competing Interests: Competing Interest Statement D.K.S. is a collaborator with Thermo Fisher Scientific, Genentech, Calico Labs, and AI Proteins. C.K.C., A.F.T., E.K., D.M.S., and B.J.B. have filed a patent application covering aspects of this work. B.J.B. is listed as an inventor on patent applications related to the SABER technology related to this work.

Aberrant proteins can be deleterious to cells and are cleared by the ubiquitin-proteasome system. A group of C-end degrons that are recognized by specific cullin-RING ubiquitin E3 ligases (CRLs) has recently been identified in some of these abnormal polypeptides. Here, we report three crystal structures of a CRL2 substrate receptor, KLHDC2, in complex with the diglycine-ending C-end degrons of two early-terminated selenoproteins and the N-terminal proteolytic fragment of USP1. The E3 recognizes the degron peptides in a similarly coiled conformation and cradles their C-terminal diglycine with a deep surface pocket. By hydrogen bonding with multiple backbone carbonyls of the peptides, KLHDC2 further locks in the otherwise degenerate degrons with a compact interface and unexpected high affinities. Our results reveal the structural mechanism by which KLHDC2 recognizes the simplest C-end degron and suggest a functional necessity of the E3 to tightly maintain the low abundance of its select substrates., (Published by Elsevier Inc.)

Imaging is broadly used in biomedical research, but signal variation complicates automated analysis. Using the Pulmonary Metastasis Assay (PuMA) to study metastatic colonization by the metastasis suppressor KISS1, we cultured GFP-expressing melanoma cells in living mouse lung ex vivo for 3 weeks. Epifluorescence images of cells were used to measure growth, creating large datasets which were time consuming and challenging to quantify manually due to scattering of light from outside the focal plane. To address these challenges, we developed an automated workflow to standardize the measurement of disseminated cancer cell growth by applying statistical quality control to remove unanalyzable images followed and a filtering algorithm to quantify only in-focus cells. Using this tool, we demonstrate that expression of the metastasis suppressor KISS1 does not suppress growth of melanoma cells in the PuMA, in contrast to the robust suppression of lung metastasis observed in vivo. This result may suggest that a factor required for metastasis suppression is present in vivo but absent in the PuMA, or that KISS1 suppresses lung metastasis at a step in the metastatic cascade not tested by the PuMA. Together, these data provide a new tool for quantification of metastasis assays and further insight into the mechanism of KISS1 mediated metastasis suppression in the lung.