Protein protection from the sun.

New information reported by researchers at the University of Texas Southwestern Medical Center in Dallas could eventually help scientists develop better ways to protect against and treat the adverse effects of too much sunlight. In a paper published in the June 1999 issue of Molecular Cell, the researchers demonstrated that the interaction between a protein called Rad23 and a protein complex known as the 26S protea-some is important for the ability of yeast cells to repair DNA damage caused by ultraviolet (UV) light. Human cells contain very similar proteins, so this finding may lead to insights into how human skin responds to UV exposure. The study built on earlier work by researchers from the Robert Wood Johnson Medical School in Piscataway, New Jersey, published in the 12 February 1998 issue of Nature, that first demonstrated a physical interaction between Rad23 and the 26S proteasome. The 26S proteasome is a large, two-part complex involved in the degradation of many different cellular proteins: the 19S regulatory complex is thought to bind to damaged proteins, unfold their Sun spot. The site of interaction between a protein and a proteasome is yielding clues to the repair of DNA damage from UV light. twisted lengths, and thread them into the barrel-shaped 20S structure, where they are degraded by protease enzymes. The site of interaction between the 26S proteasome and Rad23 appears to be Rad23's ubiquitin (Ub)-like domain, a section of the protein that physically resembles true Ub, a small protein that connects to other proteins and targets them to be degraded by the 26S proteasome. (This does not seem to be the case for the Ub-like domain of Rad23, however; its function is still not understood.) Other, earlier research had shown that yeast missing the Rad23 protein or its Ub-like domain were more sensitive to UV radiation. With the Molecular Cell study, the Texas scientists were able to show that the physical interaction between Rad23's Ub-like domain and the 26S proteasome is necessary for optimal DNA repair to take place. To investigate the relationship between Rad23 and the 26S proteasome, the researchers prepared yeast extracts that had either the Rad23 full-length protein, no Rad23 at all, or a Rad23 from which the Ub-like domain had been deleted. Yeast with the full-length Rad23 were found to repair UV damage very well. Those without the Rad23 protein displayed almost no repair activity. Those with the truncated version …