Anyone who's tried a weekend home improvement project knows that to do a job right, you've got to have the right tools. For cells, these "tools" are proteins encoded by genes. The right genes for the job are turned on only in the specific cells where they are needed. And every cell in your body has a specific job to do. Cells in your pancreas have to produce insulin, while cells in the retina of your eye must be able to sense light and color. Like using the wrong tool for the job, if the wrong genes are turned on in a cell, it can cause a real mess. Worse, in some cases it can cause serious disease like cancer. Rendering of DNA. Scientists have now shown that transcription factors don't act like an 'on-off' switch, but instead can exhibit much more complex binding behavior. Anthony Carter, PhD, who oversees gene regulation grants at the National Institutes of Health's National Institute of General Medical Sciences, explains, "By taking an interdisciplinary approach that incorporates the use of mathematical modeling tools, Dr. Lieb has shed new light on a fundamental cellular process, the ability to quickly shift between active and inactive states of gene expression. The findings may offer new insights on how cells respond to developmental cues and how they adapt to changing environmental conditions." The National Institute of General Medical Sciences partially supported the work. Other UNC authors are: Sean E. Hanlon, PhD. Additional authors are James G. McNally, PhD. and Florian Mueller, PhD, both from the Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health.