Gene expression is regulated by cells in response to internal and external signals. The lac genes in E.coli, which are responsible for the digestion of the sugar lactose, can be turned on or off depending on whether or not lactose is the only food source present. In this talk we will investigate the role of DNA mechanics in the regulation of gene expression, and in particular the effect that DNA looping has on the mean, and on the fluctuations (cell to cell variability) of the number of messenger RNAs produced from the lac genes. An interesting observation is that the mean and the fluctuations in gene expression can be tuned independently suggesting a method for engineering noisy expression systems.