 <unk> domains , or <unk> interphase <unk> associations , were first described in microscopy studies in 1991 . Their function remains unclear , though they were not thought to be associated with active DNA replication , transcription , or RNA processing . They have been found to often associate with discrete domains defined by dense localization of the transcription factor <unk> , which promotes transcription of small nuclear RNA ( <unk> ) . 
