COILED BODIES AND U2 SNRNA GENES ADJACENT TO COILED BODIES ARE ENRICHED IN FACTORS REQUIRED FOR SNRNA TRANSCRIPTION

A significant percentage of the gene clusters that contain the human g enes for U1 small nuclear RNA (snRNA) or for U2 snRNA have been found associated with small nuclear domains, known as coiled bodies. We show here, by immunofluorescent labeling of human cells, that coiled bodie s are enriched in factors required for the transcription of these snRN A genes. The 45-kDa gamma-subunit of the transcription factor, proxima l element sequence-binding transcription factor (PTF), which is specif ic for the snRNA genes, was found in high concentrations in coiled bod ies, along with the general transcription factor TATA-box binding prot ein and a subset of RNA polymerase II. We show that the transcription factors and RNA polymerase II are concentrated in irregularly shaped d omains that not only overlap with coiled bodies but also extend to the ir immediate surroundings. Fluorescent in situ hybridization showed th at these domains can overlap with U2 snRNA genes adjacent to coiled bo dies. Ln addition, we found the domains to contain newly synthesized R NA, visualized by 5-bromo-uridine triphosphate labeling. Our data sugg est that coiled bodies are involved in the expression of snRNA genes, which leads us to propose the model that coiled bodies are associated with snRNA genes to facilitate and regulate their transcription. These findings point to a general principle of higher order organization of gene expression in the nucleus.