Global chromatin compaction in response to ultraviolet radiation

Chromatin, the complex of DNA, associated proteins, and RNA has several levels of folding. Gene expression, DNA replication, and DNA repair are cellular functions dependent on unfolding compacted chromatin. This study aims to understand the relationship between UV radiation and the compaction level of chromatin within a cell. Large scale chromatin compaction after UV radiation was observed by a hybrid protein LacR-CFP tethered to a 256 tandemly repeated LacO DNA sequences integrated into the genome of NIH2/4 mouse embryonic fibroblasts. We further corroborated global chromatin compaction in human cervical cancer HeLa cells and in normal human epidermal melanocytes irradiated by UV-B, using two fluorescent dyes and we demonstrated that this compaction protects the DNA from further damage using immunostaining. We also have shown that UV-induced chromatin compaction is dependent on the influx of calcium ions into the nucleus. We currently plan to explore the pathway controlling the UV-induced calcium influx.