The ER repeat protein YT521-B localizes to a novel subnuclear compartment

The characterization of distinct subnuclear domains suggests a dynamic nucl ear framework supporting gene expression and DNA replication. Here, we show that the glutamic acid/arginine-rich domain protein YT521-B localizes to a novel subnuclear structure, the YT bodies. YT bodies are dynamic compartme nts, which first appear at the beginning of S-phase in the cell cycle and d isperse during mitosis, Furthermore, in untreated cells of the human cell l ine MCF7 they were undetectable and appeared only after drug-induced differ entiation. YT bodies contain transcriptionally active sites and are in clos e contact to other subnuclear structures such as speckles and coiled bodies . YT bodies disperse upon actinomycin D treatment, whereas other transcript ional inhibitors such as a-amanitin or DRB have little effect. On the basis of our experiments, we propose that YT521-B may participate in the assembl y of genes into transcription centers, thereby allowing efficient regulatio n of gene expression.