DSBCS modulation scheme for hybrid wireless and cable television system.

This work develops and demonstrates a double sideband with optical carrier suppression (DSBCS) modulation scheme for a hybrid wireless and cable television system based on a phase modulator (PM) and a polarization beam splitter (PBS). A carrier suppression ratio greater than 20 dB is achieved between two sidebands. In addition, the values of carrier-to-noise ratio, composite second-order and composite triple beat in various channels after 25 km of transmission are higher than the threshold value, and the power penalty of microwave signal in back-to-back and 25 km transmission perform well. Additionally, the constellation diagram of upstream signal is successfully recovered. Above results demonstrate that the proposed scheme is highly promising for practical applications.

Purification of the human immunodeficiency virus type 1 enhancer and TAR binding proteins EBP-1 and UBP-1.

Transcription of the human immunodeficiency virus type 1 (HIV-1) is regulated by viral proteins and cellular factors that bind to the viral long terminal repeat (LTR). At least five regions of the HIV LTR serve as binding sites for HeLa cellular proteins. One region containing two copies of the sequence GGGACTTTCC functions as an enhancer element for HIV transcriptional regulation. Another region between -17 and +44 known as the TAR region contains two copies of the sequence CTCTCTGG and is also important in tat-induced activation of the HIV LTR. HeLa cell extracts were used to purify cellular proteins binding to portions of the enhancer region (EBP-1) and the TAR region (UBP-1) by a combination of conventional and DNA affinity chromatography. Several species of proteins of between 55 and 60 kd were found to bind to specific sequences in the enhancer region and these proteins also bound to a portion of the NF-kappa B binding site in the immunoglobulin kappa enhancer. Two proteins of between 61 and 63 kd were the major species found to bind to specific sequences in the TAR region and fractions containing these proteins also bind to the TATA region. Both UBP-1 and EBP-1 exhibited specific binding as demonstrated by both UV cross-linking and DNase I footprinting. Mutations of either the enhancer or TAR regulatory regions prevented binding of these purified factors. These results demonstrate the binding of highly purified cellular proteins to important transcriptional regulatory regions in the HIV LTR.

Interactions of cellular proteins involved in the transcriptional regulation of the human immunodeficiency virus.

The human immunodeficiency virus (HIV) is a human retrovirus which is the etiologic agent of the acquired immunodeficiency syndrome. To study the cellular factors involved in the transcriptional regulation of this virus, we performed DNase I footprinting of the viral LTR using partially purified HeLa cell extracts. Five regions of the viral LTR appear critical for DNA binding of cellular proteins. These include the negative regulatory, enhancer, SP1, TATA and untranslated regions. Deletion mutagenesis of these binding domains has significant effects on the basal level of transcription and the ability to be induced by the viral tat protein. Mutations of either the negative regulatory or untranslated regions affect factor binding to the enhancer region. In addition, oligonucleotides complementary to several of the binding domains specifically compete for factor binding. These results suggest that interactions between several distinct cellular proteins are required for HIV transcriptional regulation.

Repeated B motifs in the human immunodeficiency virus type I long terminal repeat enhancer region do not exhibit cooperative factor binding.

The enhancer element of the human immunodeficiency virus type I (HIV-I) long terminal repeat (LTR) contains two copies of nearly identical sequences AGGGACTTTCC (3G sequence) and GGGGACTTTCC (4G sequence) that are important in transcriptional regulation. A single copy of the 4G sequence is found in the NF-kappa B site of the immunoglobulin kappa-chain enhancer. Only the 4G motif in the HIV enhancer is bound by cellular proteins in extracts prepared from unstimulated HeLa cells, whereas the 3G and 4G motifs are bound by factors in extracts prepared from HeLa cells treated with phorbol esters [phorbol 12-myristate 13-acetate (PMA)] and lymphoid cells. To determine if this change in binding to the HIV enhancer was due to phosphorylation of a cellular protein, partially purified PMA-treated HeLa nuclear extracts were digested with calf intestinal phosphatase. Phosphatase digestion of nuclear extracts from PMA-treated HeLa cells markedly decreased factor binding to the HIV enhancer. Accordingly, phosphorylation of the DNA binding protein itself, or an inhibitor protein present in the partially purified extract, must mediate binding to the recognition sequence. Binding studies confirmed that each of the enhancer sequences was capable of binding factors independent of the activity of the other site and that the HIV enhancer was occupied by only one factor at any one time. Chloramphenicol acetyltransferase assays using mutants in either one or both HIV enhancer repeats revealed that each site was capable of functioning as a tat-inducible enhancer element in PMA-treated HeLa cells. These results suggest that the 3G and 4G motifs in the HIV enhancer function independently and that duplication in the HIV enhancer augments activity by a mechanism distinct from cooperative binding of NF-kappa B.