Upstream activating sequence

About: Upstream activating sequence is a research topic. Over the lifetime, 1633 publications have been published within this topic receiving 100112 citations.

Transcriptional activation by protein-induced DNA bending: evidence for a DNA structural transmission model.

Abstract: Integration host factor (IHF) is a DNA-bending protein that binds to an upstream activating sequence (UAS1) and, on a negatively supercoiled DNA template, activates transcription from the ilvPG promoter of the ilvG-MEDA operon of Escherichia coli. The transcriptional initiation site of the ilvGMEDA operon is located 92 bp downstream of UAS1. Activation is still observed when the orientation of the upstream IHF binding site is reversed. This manipulation places the IHF binding site on the opposite face of the DNA helix, directs the IHF-induced DNA bend in the opposite direction, and presents the opposite face of the nonsymmetrical, heterodimeric, IHF molecule to the downstream RNA polymerase. Lymphoid enhancer-binding factor, LEF-1, is a DNA-bending, lymphoid-specific, mammalian transcription factor that shares no amino acid sequence similarity with IHF. When the IHF site in UAS1 is replaced with a LEF-1 site, LEF-1 activates transcription from the downstream ilvPG promoter in E. coli as well as it is activated by its natural activator, IHF. These results suggest that specific interactions between IHF and RNA polymerase are not required for activation. The results of DNA structural studies show that IHF forms a protein-DNA complex in the UAS1 region that, in the absence of RNA polymerase, alters the structure of the DNA helix in the -10 hexanucleotide region of the downstream ilvPG promoter. The results of in vitro abortive transcription assays show that IIIF also increases the apparent rate of RNA polymerase isomerization from a closed to an open complex. We suggest, therefore, that IHF activates transcription by forming a higher-order protein-DNA complex in the UAS1 region that structurally alters the DNA helix in a way that facilitates open complex formation at the downstream ilvPG promoter site.

Hepatocyte-specific expression of the hepatitis B virus core promoter depends on both positive and negative regulation.

Abstract: The core promoter of hepatitis B virus shows hepatocyte specificity, which is largely dependent on an upstream regulatory sequence that overlaps with viral enhancer II. Footprint analyses by numerous groups have shown binding by cellular proteins over a large stretch of DNA in this region, but the identity of these proteins and their role in core promoter function remain largely unknown. We present data showing that the transcription factor HNF-4 is one such factor, as it activates the core promoter approximately 20-fold via a binding site within the upstream regulatory sequence. Since HNF-4 is enriched in hepatocytes, its involvement at least partially explains the hepatocyte specificity of this promoter. In addition, however, we have found a region upstream of the HNF-4 site that suppresses activation by HNF-4 in HeLa cells but not in hepatoma cells. Therefore, the cell type specificity of the core promoter appears to result from a combination of activation by one or more factors specifically enriched in hepatocytes and repression by some other factor(s) present in nonhepatocytes, and it may provide a convenient model system for studying this type of tissue-specific transcriptional regulation in mammalian cells.

The primary structure and expression of four cloned human histone genes

Abstract: The complete nucleotide sequence of four human histone genes has been determined. Each gene codes for a core histone protein which is very homologous with the corresponding calf thymus of rat histones. The 5' and 3' flanking regions of the human histone genes contain previously identified concensus sequences: the TATA box, the GACTTC element; the CCAAT sequence; the 3' terminal dyad symmetry element thought to be involved in transcription termination; and a recently identified H2b specific upstream sequence. A putative H2a specific upstream sequence 5'-TTCTTGGACTCCTCTTTTC-3' is present approximately 40 base pairs upstream from the TATA box in the human H2a gene promoter. Nuclease S1 analysis of the human histone mRNAs encoded within each of these clones demonstrates that the mRNA terminii map to the expected positions relative to the known concensus sequences, and that the abundance of each mRNA is regulated during the HeLa cell cycle. Finally, in contrast to the H2b, H3 and H4 mRNAs encoded within clones pHh 4A/pHh4C, pHh5B and pHu4A, respectively, the H2a mRNA encoded by Hh5G is not present in human placental RNA.