The UPR that is induced by abnormally high or low concentrations of sugar is linked to the production of ROS, increased apoptosis in LECs, and cataract formation. The inhibition of the UPR induction by ARI suggests that osmotic stress may be the primary inducer of the UPR. Modulation of the UPR pathways may offer novel methods for the development of therapeutic tools to delay cataracts.

We constructed two site-specifically modified nucleosomes containing an intrastrand cis-{Pt(NH3)2} 2؉ 1,3-d(GpTpG) cross-link, similar to one formed by the anticancer drugs carboplatin and cisplatin on DNA, and investigated their structures by hydroxyl radical footprinting and exonuclease III digestion. Hydroxyl radical footprinting demonstrated that the presence of the platinum cross-link selects out a specific rotational setting of DNA on the histone octamer core in each of two reconstituted nucleosomes in which the platinum positions differ by half a DNA helical turn. The {Pt(NH3)2} 2؉ cross-link is situated in a structurally similar location, with the undamaged strand projecting outward, forcing the DNA to adopt opposite rotational settings in its wrapping around the histone octamer in the two nucleosomes. Enzymatic digestion by exonuclease III of the nucleosome substrates revealed that the platinum cross-link affects the translational positioning of the DNA, forcing it into an asymmetric arrangement with respect to the core histone proteins. We suggest that these phasing phenomena may be central to the recognition and processing of platinum-DNA adducts in cancer cells treated with these drugs and possibly may be common to other DNA damaging events.cancer ͉ carboplatin ͉ chromatin ͉ DNA repair ͉ DNA structure T he anticancer drugs cisplatin and carboplatin form intrastrand cross-links on DNA that evoke their antineoplastic activity by inhibiting DNA and RNA polymerases while escaping resistance mechanisms including nucleotide excision repair (NER) (1). In the cell, recognition of the platinum lesion by the repair machinery in the context of chromatin may require exposure of the damaged DNA duplex to the exterior of the nucleosome.The nucleosome is the fundamental building block of chromatin. Nature has therefore constructed it in such a manner as to lack a preferred positional setting for most sequences of the double-stranded DNA that wraps around the central core of eight histone proteins (2, 3). The rotational setting of DNA on the surface of the histone octamer defines which nucleotides are directed toward the solvent and which are occluded by the histones.Determining where platinum-DNA cross-links are located within the nucleosome represents an important step in understanding their cellular recognition and processing. A key question is whether the platinum adduct or the DNA sequence determines the rotational setting of a DNA segment on the nucleosome and therefore how the platinum lesion is presented to the replication, transcription, and repair machinery of the cell. To answer this question, we prepared two nucleosomes in which a 1,3-d(GpTpG) cross-link was incorporated site-specifically near the center of the DNA molecule. The sites of platination were placed one-half turn of the DNA helix apart in the two nucleosomal DNA sequences. We then used high-resolution footprinting and exonuclease mapping experiments to reveal the rotational and translational settings of the platinated DNA in the two nucleosom...