Direct quantification of gene expression using fluorescence correlation spectroscopy

Among the methods for single molecule detection in the field of medicinal chemistry, the importance of fluorescence correlation spectroscopy (FCS) is growing. FCS has the advantage of permitting us to determine the number of fluorescent molecules and the diffusion constant dependent on the molecular weight without any physical separation process such as gel electrophoresis. Thus this method is appropriate for studies on the hybridization of fluorescence-labeled oligonucleotides with RNA or DNA as well as gene expression through translation of a target protein linked with green fluorescent protein. Indeed, several groups have employed FCS for evaluation of gene expression in different ways. Many investigators are particularly interested in using FCS to quantitatively analyze mRNA just after transcription in the living cell. Technical advances in FCS have broadened the research spectrum in medicinal chemistry since it can also be used to study SNPs and molecular interactions between transcription factors and promoter sequences, as well as gene expression in living cells.