Effect of UV irradiation on Sulfolobus acidocaldarius and involvement of the general transcription factor TFB3 in early UV response

Extremophilic archaea like all organisms experience potentially life-threatening conditions including UV light, which induces severe DNA damage. Since the alternative general transcription factor (GTF) TFB3 has been proposed to play a key role in UV stress response in the thermoacidophilic crenarchaeon Sulfolobus acidocaldarius, we investigated the expression of TFB3 on protein level including in vivo protein-protein interaction studies, tfb3 reporter gene assays and creation of a tfb3 insertion mutant to study early differential gene expression upon UV treatment (after 45 and 90 minutes). Our results allowed differentiating between the TFB3-dependent and TFB3-independent early UV response in S. acidocaldarius. The early TFB3-independent UV response includes the repression of nucleotide biosynthesis and transport, replication and cell cycle progression in order to allow DNA repair. The TFB3-dependent UV response is characterized by the early induction of TFB3, which is a prerequisite for the following TFB3-dependent expression of genes involved in ups pili formation and the Ced DNA importer. Both structures facilitate the transfer of DNA to allow repair via homologous recombination. The fact, that all genes are downregulated in the tfb3 mutant compared to the reference strain, confirms the hypothesis that TFB3 acts as an activator of transcription.