Alignment of 5′LTR nucleotide sequences of BLV strains. BLV strains isolated from PBMC cells and previously described are shown by accession number on the left side of the figure. BLV isolates from B-lymphosarcoma tumors (LS1 through LS3) are shown by name. Identity with BLV strain LS1 is indicated by a dot. The U3, R, and U5 regions are indicated on top of the alignment. The three TxRE enhancer regions are shown in green, cyclic AMP- responsive element (CRE) sequences are underlined and E-Box sequences are shown in italics. Binding sites for PU.1/Spi-B are shown in bold. The glucocorticoid responsive element (GRE) binding site is shown in bold, italics and underlined. Nuclear factor κB (NF-κB) binding sites are shown double underlined. The CAT box and GATAA box promoters (PROMT) sequences are indicated in yellow and in bold italics, respectively. The polyadenylation site (PAS) is shown in magenta and the CAP site is shown in light blue. The tRNA proline primer binding sites are shown in red. The downstream activator sequence (DAS) and the interferon regulatory factor (IRF) binding sites are shown in dark and light grey, respectively.