Fig. 2

Model of BLV 5ʹLTR latency and transcriptional activation. A During latency, the BLV 5ʹLTR promoter activity is repressed by genetic (not shown) and epigenetic mechanisms. These epigenetic mechanisms include the hypermethylation of the DNA and the hypoacetylation of the histone tails due to the recruitment of the histone deacetylase 1 (HDAC1) and the co-repressor mSin3A. B Transcriptional initiation might occur by external stimuli or the use of epigenetic drugs. The pioneer transcription factor PU.1 could participate in the opening of the chromatin, increasing the accessibility of cis-regulatory elements to other transcription factors such as IRFs, USFs and CREB/ATF factors and the associated co-activators CBP/p300. C Once the transcription is initiated, the viral transactivator Tax is produced and directly interacts with CREB/ATF factors increasing their binding affinity for the Tax-responsive elements (TxREs), thereby resulting in strong expression of the viral genes