Sp1 family proteins recognize the U5 repressive element of the long terminal repeat of human T cell leukemia virus type I through binding to the CACCC core motif.
We have identified several nuclear proteins binding to the U5 repressive element (U5RE) at the U5 region of the human T cell leukemia virus type I (HTLV-I) long terminal repeat (LTR). In gel mobility shift assays with the U5RE DNA probe, Jurkat T cell nuclear proteins generated five different complexes, named U5RE binding protein complexes (U5RP)-A1, -A2, -A3, -B, and -C. Only U5RP-C was affected by pretreatment with an excess of poly(dI-dC) and was immunodepressed by anti-Ku/p80 antibodies, suggesting that U5RP-C is a nonspecific complex involving Ku antigen. UV cross-linking showed at least six nuclear proteins involved in the other complexes, including U5RP-A1, -A2, -A3, and -B. The sequence of the binding core element of these specific complexes, determined by competition assays and gel mobility shift assays using a series of the U5RE mutants, is CACCC which is identical to that for the Sp1 transcription factor. LTR with a mutant U5RE, which has no ability to bind with the nuclear proteins, showed stronger promoter activity than LTR with the wild U5RE, suggesting that the specific interaction of these U5RE-binding proteins might result in the U5-mediated repression. U5RP-A1 was supershifted by anti-Sp1 antibodies and U5RP-A2 and -B were supershifted by anti-Sp3 antibodies, suggesting that Sp1 or Sp3 is involved in U5RP-A1 or U5RP-A2 and -B, respectively. Although the other nuclear proteins remain to be characterized, these findings suggest that U5RE-binding proteins in U5RP-A1, -A2, -A3, and -B are involved in HTLV-I gene repression.
Okumura
K
K
Shionogi Institute for Medical Science, 2-5-1 Mishima, Settsu, Osaka 566, Japan.
Sakaguchi
G
G
Takagi
S
S
Naito
K
K
Mimori
T
T
Igarashi
H
H
D001483:Base Sequence; D002460:Cell Line; D004279:DNA, Viral; D015368:Human T-lymphotropic virus 1 / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding; D012091:Repetitive Sequences, Nucleic Acid; D016329:Sp1 Transcription Factor / Q000378:metabolism*
D004279:DNA, Viral; D016329:Sp1 Transcription Factor