Characterization of trans-acting factor(s) involved in Marek's disease virus (MDV) mediated transactivation of rous sarcoma virus (RSV) long terminal repeat (LTR) promoter

Trans-acting factor(s) responsible for MDV-mediated RSV-LTR promoter activation forms a unique DNA-protein complex with sequences contained within a 25 bp LTR region, known as the pentanucleotide repeat element(PRE). Previous results have demonstrated that the PRE: is essential for MDV-mediated RSV-LTR transactivation. However, the nature of factors interacting with PRE regions in both MDV-infected and uninfected cells are largely unknown. To further examine factors binding to this region of the RSV-LTR and interactions between MDV-encoded and cellular proteins, we applied southwestern blot assay, electrophoretic mobility shift competition assays and transient expression assays using RSV-LTR PRE region probes. Our results suggest that MDV-encoded trans-acting factors associate with PRE regions indirectly through interactions with two cellular factors. Both cellular transcription factors are essential for RSV-LTR promoter basal activity. One factor binds to a previously characterized EFI site while the second factor appears to be related to the cellular ets family of transcription factors.