The human genome contains numerous clusters of adjacent co-regulated genes

A major aim in the postgenomic era is the global understanding of the orchestrated gene expression activity and its relation with the architecture of the intranuclear space. We report that approx. 15% of the human genes are located within clusters of 3-20 neighboring genes that present high frequency of correlated expression with members of the same cluster. The clusters are present in all chromosomes and the gene density is higher within clusters versus the intercluster regions. The genes within each cluster do not have obvious functional connections. The magnitude of correlations within clusters does not depend on the distance between genes, suggesting a mechanism that acts uniformly over the cluster span. The clusters are different than the groups of highly expressed or the groups of housekeeping genes identified in the human genome, and may correspond to the previously identified Drosophila domains of similarly expressed genes. The correlations are significantly stronger within clusters versus the intercluster regions, and the clustered genes are more frequently correlated not only with genes within but also with genes outside their cluster.