Protein-DNA interactions at the Sulfolobus spindle-shaped virus-1 (SSV1) T5 and T6 gene promoters.

Ultraviolet irradiation upregulates transcription from the Sulfolobus spindle-shaped virus 1 (SSV-1) T5, T(ind), and T6 genes promoters and also triggers viral DNA replication, but nothing is known about the proteins involved in this process. A notable feature of T5 and T6 promoters is that they contain 4 copies of a highly conserved DNA sequence 5'-ATAGATAGAGT-3'; 2 copies of this repeat are found in tandem upstream of the A-box, whereas 2 additional tandem copies span the initiator region from which transcription originates. By employing electrophoretic mobility gel-shift assays (EMSAs) and chemical modification interference analyses, I have identified a protein STRIP (SSV-1 T5/T6 region-interacting protein) in Sulfolobus shibatae extract that binds specifically to this sequence. Unique to S. shibatae, STRIP induces a 28 degrees bend in DNA. Surprisingly, despite the fact that STRIP binding masks the initiator region and can potentially interfere with preinitiation complex assembly, it does not appear to effect transcription driven from T5 and T6 promoters in vitro. Based on these results, I discuss the potential roles of STRIP in T5 and T6 transcription and in initiating SSV-1 DNA replication.