Yin Yang 1 (YY1) is a DNA-binding transcription factor that either activates or represses gene expression. YY1 has previously been implicated in the transcriptional silencing of many retroviruses by binding to DNA sequences in the U3 region of the viral long terminal repeat (LTR). We here show that YY1 overexpression leads to profound activation, rather than repression, of human T lymphotropic virus type 1 (HTLV-1) expression, while YY1 down-regulation reduces HTLV-1 expression. The YY1 responsive element mapped not to YY1 DNA-binding sites in the HTLV-1 LTR but to the R region. The HTLV-1 R sequence alone is sufficient to provide YY1 responsiveness to a nonresponsive promoter, but only in the sense orientation and only when included as part of the mRNA. YY1 binds to the R region of HTLV-1 RNA in vitro and in vivo, leading to increased transcription initiation and elongation. The findings indicate that YY1 is a potent transactivator of HTLV-1 gene expression acting via binding viral RNA, rather than DNA.

阴阳1（YY1）是激活或抑制基因表达的DNA结合转录因子。YY1以前通过与病毒长末端重复序列（LTR）的U3区域中的DNA序列结合，参与了许多逆转录病毒的转录沉默。我们在这里显示YY1的过表达导致人类T淋巴病毒1型（HTLV-1）表达的深入激活，而不是抑制，而YY1下调降低了HTLV-1的表达。YY1响应元件不是映射到HTLV-1 LTR中的YY1 DNA结合位点，而是映射到R区。单独的HTLV-1 R序列足以提供对无应答启动子的YY1应答，但仅在有义方向上且仅当作为mRNA的一部分包含时才如此。YY1在体内和体外均与HTLV-1 RNA的R区结合，导致转录起始和延伸增加。研究结果表明，YY1是通过结合病毒RNA而非DNA起作用的HTLV-1基因表达的有效反式激活因子。