RNA polymerase II and III transcription factors can stimulate DNA replication by modifying origin chromatin structures.

Many transcription factors are multifunctional and also influence DNA replication. So far, their mechanism of action has remained elusive. Here we show that a DNA-binding protein could rely on the same biochemical activity that activates transcription to stimulate replication from the yeast chromosomal ARS1 origin. Unexpectedly, the ability to stimulate replication from this origin was not restricted to polymerase II transcription factors, but was a property shared by polymerase III factors. Furthermore, activation of replication did not depend on the process of transcription, but rather on the ability of DNA-binding transcription factors to remodel chromatin. The natural ARS1 activator Abf1 and the other transcription factors that stimulated replication remodeled chromatin in a very similar manner. Moreover, the presence of a histone H3 mutant that was previously shown to generally increase transcription also facilitated replication from ARS1 and partially compensated for the absence of a transcription factor. We propose that multifunctional transcription factors work by influencing the chromatin architecture at replication origins so as to generate a structure that is favorable to the initiation of replication.

Conservation of glutamine-rich transactivation function between yeast and humans.

Several eukaryotic transcription factors such as Sp1 or Oct1 contain glutamine-rich domains that mediate transcriptional activation. In human cells, promoter-proximally bound glutamine-rich activation domains activate transcription poorly in the absence of acidic type activators bound at distal enhancers, but synergistically stimulate transcription with these remote activators. Glutamine-rich activation domains were previously reported to also function in the fission yeast Schizosaccharomyces pombe but not in the budding yeast Saccharomyces cerevisiae, suggesting that budding yeast lacks this pathway of transcriptional activation. The strong interaction of an Sp1 glutamine-rich domain with the general transcription factor TAF(II)110 (TAF(II)130), and the absence of any obvious TAF(II)110 homologue in the budding yeast genome, seemed to confirm this notion. We reinvestigated the phenomenon by reconstituting in the budding yeast an enhancer-promoter architecture that is prevalent in higher eukaryotes but less common in yeast. Under these conditions, we observed that glutamine-rich activation domains derived from both mammalian and yeast transcription factors activated only poorly on their own but strongly synergized with acidic activators bound at the remote enhancer position. The level of activation by the glutamine-rich activation domains of Sp1 and Oct1 in combination with a remote enhancer was similar in yeast and human cells. We also found that mutations in a glutamine-rich domain had similar phenotypes in budding yeast and human cells. Our results show that glutamine-rich activation domains behave very similarly in yeast and mammals and that their activity in budding yeast does not depend on the presence of a TAF(II)110 homologue.