The architecture of DNA in the interior of the living cell nucleus is an emerging key contributor to genomic function. Aim of our research is to understand the relationship between chromosome folding and gene expression in mammalian cells. We combine high-resolution microscopy techniques with 4C technology, a novel high-throughput genomics approach recently developed in our laboratory. 4C technology uniquely allows screening the entire genome for DNA regions that interact with a DNA segment of choice. As such, it is expected to importantly contribute to our understanding of nuclear architecture.