Transcription factories
February 7, 2008 by vidhyaj
Today we had a very fascinating story by Peter Fraser (from the Babraham Institute, Cambridge), suggesting that genes migrate to specialized sites called transcription factories in the nucleus for transcription. These transcription factories are nothing but discrete foci in the nucleus containing high concentrations of RNA polII(the eukaryotic polymerase responsible for transcription of protein-coding genes). This is very much opposed to the well known text book theory that the RNA polymerase is recruited to promoters and RNA are transcribed from de novo transcription start sites.
The number of discrete factories visible in the nucleus is less than the number of expressed genes, which means that multiple genes are transcribed from one factory. This is also evident from the fact that the hbb(hemoglobin beta chain- a component of oxygen carrying hemoglobin protein in blood) gene is transcribed in the same factory as that other similarly expressed genes in the erythroid cell. These genes are seperated by more than 50 megabases in cis(present of the same chromosome). Also unlinked genes in trans(present on different chromosomes) co-localized in the same the transcription factory but the frequency of such co-localization was low. (ex hbb & hba genes). The most interesting fact was that the quiet allele of active genes are located away from the transcription factories.
He also discussed more about the nuclear co-localization and regulatory functional implication of such localizations, described in detail in ” Nuclear organization of the genome and the potential for gene regulation Nature. 2007 May 24;447(7143):413-7”
The interacting cis and trans genes completely dissociated when RNA initiation was inhibited by heat-shocking cells at 45 degrees, while the remained associated when only the RNA elongation was inhibited using a chemical DRB. Futhermore the transcription factories persisted even in the absence of transcription Which he presented as a compelling evidence that these transcription factories are distinct nuclear sub-compartments and not just local concentrated foci of RNA pol II. ref:” Transcription factories are nuclear subcompartments that remain in the absence of transcription Mitchell JA, Fraser P 2008 Jan 1;22(1):20-5“
