\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,amstext,amsopn,amscd,amsfonts}
\pagestyle{empty}
\begin{document}
\begin{displaymath}PoPsOUT = \frac{nbGenesCopies*maxTranscriptionRate*[activator]^{n}}{K^{n} + [activator]^{n}}\end{displaymath}
\end{document}
