Modulation of interferon gene transcription by positive and negative cellular factors

In vivo competition experiments were designed to identify the role of trans-acting cellular factors in the virus-inducible activation of the interferon-beta promoter. Co-transfection of a constant amount of IFN-beta/CAT test gene and increasing amounts of competitive DNA containing different IFN regulatory domains into human epithelioid 293 cells identified a low abundance, positive cellular factor(s) that interacts with the IFN regulatory region. Competition of the factor decreases virus-induced and constitutive level expression of the IFN-beta promoter, and also partially inhibits expression from the SV40 promoter. Negative regulatory effects produced by factors interacting with the IFN upstream region (-135 to -202) and with the SV40 enhancer were also observed.     

Reconciling the positive and negative roles of histone H2A.Z in gene transcription

The incorporation of variant histone H2A.Z within chromatin is important for proper gene expression and genome stability. H2A.Z is inserted at discrete loci by the Swr1 or Swr1-like remodeling complexes, although very little is known about the nature of the targeting mechanism involved. Replacement of canonical histone H2A for H2A.Z has been shown to modify nucleosome dynamics, although discrepancies still exist in the literature regarding the mechanisms. Recent experiments have shown that H2A.Z can allow nucleosomes to adopt stable translational positions as compared to H2A, which could influence the accessibility to DNA regulatory proteins. This review provides a brief overview of H2A.Z biology and presents hypotheses that could reconcile contradictory reports that are found in the literature regarding the influence of H2A.Z on nucleosome stability.