HBZ and adult T-cell leukemia/lymphoma: In contrast to the sporadic expression of viral transactivator protein Tax (encoded by the sense strand of the provirus and transcribed from the 5′ LTR), HBZ (HTLV-1 bZip factor) protein (encoded by the antisense strand of the provirus and transcribed from the 3′ LTR) is consistently detected in most infected cells and leukemic cells from ATLL patients (Satou et al., 2006).