TRANSCRIPTION Reverse Recruitment of DNA

Menon et al. have proposed an intriguing model for transcriptional activation in yeast in which DNA moves to a platform of assembled components of the transcriptional machinery anchored to nuclear pore proteins. In Saccharomyces cerevisiae, Rap1 (repressor/activator protein 1), Gcr1, and Gcr2 form a complex that activates transcription of glycolytic and translational component genes. Synthetic genetic array analysis, in which the combined effects on synthetic growth of deletion of the gene encoding Gcr1 or Gcr2 and deletion of each of about 4700 different yeast genes were assessed, revealed a functional link between the Rap1 complex and components of the nucleoporin Nup84 nuclear pore subcomplex. Western analysis indicated that Rap1, Gcr1, and Gcr2 were enriched in nuclear envelope fractions, whereas coimmunoprecipitation demonstrated association of Gcr1 and Gcr2 with Nup84 and two other nuclear pore proteins and with a β-importin associated with the nuclear pore complex. Fusion proteins in which Nup84, other members of the Nup84 subcomplex, or two other nucleoporins were combined with a heterologous DNA binding domain transcriptionally activated a gene reporter. Fluorescent labeling of Nup84 and Nup85 fusion proteins indicated that this transcriptional activation occurred at the nuclear periphery. Transcriptional activation by nucleoporins depended on expression of gcr1 and gcr2, whereas transcriptional activation by Gcr1 and Gcr2 was impaired by the lack of nup84. Thus, the authors conclude that transcriptional activation by Rap1 occurs through a protein complex at the nuclear periphery and speculate on the possibility that transcriptional activation by nucleoporins—and "reverse recruitment" of DNA--may be widespread phenomena.

B. B. Menon, N. J. Sarma, S. Pasula, S. J. Deminoff, K. A. Willis, K. E. Barbara, B. Andrews, G. M. Santangelo, Reverse recruitment: The Nup84 nuclear pore subcomplex mediates Rap1/Gcr1/Gcr2 transcriptional activation. Proc. Natl. Acad. Sci. U.S.A. 102, 5749-5754 (2005). [Abstract] [Full Text]