Increased levels of E2F-1-dependent DNA binding activity after UV- or gamma-irradiation.

In mammalian cells, DNA damage induces robust changes in gene expression and these changes contribute to the proper execution of cellular responses to DNA damage, including DNA repair, cell cycle arrest and apoptosis. The transcription factor E2F-1 has been suggested to play a key role in the regulation of cell cycle-dependent gene expression and apoptosis. These activities depend on the ability of E2F-1 to form functionally active DNA binding complexes. Here we describe an assay that allows one to measure E2F-1 DNA binding activity in naive cells. We find that DNA damage, generated by UV- or gamma-irradiation, prompts increased production of E2F-1 DNA binding activity, which, at least in part, originates from alterations in E2F-1 protein levels. These findings represent an indication for a role of the transcription factor E2F-1 in the DNA damage response pathway.

Transcriptional activation modulated by homopolymeric glutamine and proline stretches.

Many transcription factors contain proline- or glutamine-rich activation domains. Here it is shown that simple homopolymeric stretches of these amino acids can activate transcription when fused to the DNA binding domain of GAL4 factor. In vitro, activity increased with polymer length, whereas in cell transfection assays maximal activity was achieved by 10 to 30 glutamines or about 10 prolines. Similar results were obtained when glutamine stretches were placed within a [GAL4]-VP16 chimeric protein. Because these stretches are encoded by rapidly evolving triplet repeats (microsatellites), they may be the main cause for modulation of transcription factor activity and thus result in subtle or overt genomic effects.