• Journal of Microbiology
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• v.37 no.3
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• pp.175-179
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• 1999

To elucidate the role of vir-box in the expression of the virE gene, the vir-box was modified by site-directed mutagenesis and tested for ${\beta}$-galactosidase activities. A, C, T T, A, C substitutions at -62, -63, and -65 positions, destroying the 5'-region of the vir-box and A T at position -55, destroying the 3'-region of the vir-box respectively, showed only 17% promoter activity. When the vir-box was modified to contain perfect dyad symmetry structure (DSR) by the substitutions T, G A, T at -60 an d-61 positions, ${\beta}$-glactosidase activity increased 302%. These results indicate that the 5' and 3'-region of vir-box as well as the imperfect DSR of the vir-box itself may play a very important role in the regulation of virE gene expression.

• Journal of Plant Biology
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• v.38 no.3
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• pp.259-266
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• 1995

To investigate how the dyad symmetry region (DSR) and the distance between vir box and -35 sequence of the virE promoter plays a role in virE gene expression, two mutants were constructed by base substitution and insertional mutagenesis. The base substitutional mutation, a AAlongrightarrowCG substitution at positions -39 and -40 on the DSR, showed the level of $\beta$-galactosidase activity approximately 91% of the wild type virE promoter activity. Therefore, the native structure of the DSR seems to be not essential for virE expression. The insertional mutation, constructed by inserting 8 bp ClaI linker between -49 and -50, displayed the $\beta$-galactosidase activity at 12% of the native virE promoter activity. However, this striking reduction appears to be not caused by destruction of the native DSR structure, but by shifting the vir box far from putative -35 sequence.

• Proceedings of the Botanical Society of Korea Conference
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• 1987.07a
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• pp.149-155
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• 1987

Growth and development of a higher plant, or any living organism for that matter, could be defined as an orderly expression of the genome in time and space in close interaction with the environment. During differentiation and development of a tissue or organ a group of genes must be selectively turned on or turned off mainly by trans-acting regulators. In this general concept of regulation of regulation of gene expression, a DNA molecule is recognized at a specific nucleotide sequence by DNA-binding factors. Molecular biology of the regulatory factors such as hormones, and their receptors, target DNA sequences and DNA-binding proteins are well advanced. What is not clearly understood is the molecular basis of the interactions between DNA and binding factors, expecially of the usages of the dyad symmetry of the target DNA sequences and the dimeric nature of the DNA-binding proteins. A unique 3-dimensional structure of DNA has been proposed that may play an important role in the orderly expression of the gene. A foldback intercoil (FBI) DNA configuration which was originally found by electron microscopy among mtDNA molecules from pearl millet has some unique features. The FBI configuration of DNA is believed to be formed when a flexible double helix folds back and interwines in the widened major grooves resulting in a four stranded, intercoil DNA whose thickness is the same as that of double stranded DNA. More recently, the FBI structure of DNA has been also induced in vitro by a novel enzyme which was purified from pearl millet mitochondria. It has been proposed that the FBI DNA could be utillized in intramolecular recombination which leads to inversion or deletion, and in intermolecular recombination which can lead to either site-specific recombination, genetic recombination via single strand invasion, or cross strand recombination. The structure and function of DNA in 3-dimensional aspect is emphasized for better understanding orderly expression of genes during growth and development.

• Korean Journal of Plant Tissue Culture
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• v.24 no.1
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• pp.1-35
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• 1997

Fertilized egg, by successive cell divisions, differentiates into different tissues and organs with various structures and functions. Different cells and tissues contain different proteins, products of selective gene expression. Not all the genes in any genomes are equally active, temporal and spatial gene expression being the general rule. Present paper attempts to review the tanscriptional mechanisms or the initiations of transcription from several angles. In some of the organisms the genes in the process of transcription or the genes in the inactive state can be seen under the light microscope. Some bands of Drosophila polytene chromosomes may exhibit a swollen or puff appearance under certain conditions. A puff, unfolded or decondensed form of chromomere, represents sets of intense transcriptional activity or RNA synthesis. The heterochromatic X chromosome whose genes remain inactive in the female mammals can be visualized as a dark staining structure called Barr body, Configuration of chromatin differs between transcribed and nontranscribed chromatin. Modification to the chromatin facilitates RNA synthesis. The movement of large polymerase molecule along the DNA would probably be facilitated if some modifications of the chromatin configuration is effected. Methylation of cytosines in CG sequences is associated with inactive genes. Methylation can play a role in determination of mammalian cells during embryogenesis. Demethylation is necessary for the gene to be expressed during development A histone modification that is also known to be correlated with transcriptional capacity of chromatin is acetylation of the lysine residues of the core histones. Chromatin containing a high level of histone acetylation is very sensitive to DNase 1. For the transcription to occur TBP must first bind to the TATA box. Another TF, TF IIB, then binds to the promoter-TBP complex, facilitating the access of RNA polymerase to the transcription initiation site. As recently as eight years ago researchers assumed that histones were irrelevant to the regulation of gene expression. Histones combine with the DNA to form nucleosome of the chromatin. Histones are vital participant in gene regulation. Histone and basal factors compete for access to TATA box. When DNA is exposed to basal factors before histones are introduced, the basal factors assemble on TATA boxes preventing the access of histones, allowing transcription to occur, for transcription to begin, activator protein at the upstream activation sequence or enhancer must interact with the tail of histone H4 at TATA box and cause the histone role particle to dissociate from the TATA box leading to partial breakup of the histone core particle and allowing the basal factors to bind to the TATA box. New concept of genomic flux in contrast to the old concept of static genome has been developed based on the powerful new molecular techniques. Genomic changes such as repetitive DNAs and transposable elements, it is assumed but not yet proved, may affect some of the developmental patterns that characterize particular cells, tissues, organs, and organisms. In the last decade or so remarkable achievement have been made in the researches of the structures and functions of TFs and the specific target sequences located in promoters or enhancers where these TFs bind. TFs have independent domains that bind DNA and that activate transcription. DNA binding domain of TFs serves to bring the protein into the right location. There are many types of DNA binding domains. Common types of motifs can be found that are responsible for binding to DNA. The motifs are usually quite short and comprise only a small part of the protein structure. Steroid receptors have domains for hormone binding, DNA binding, and activating transcription. The zinc finger motif comprises a DNA binding domain. Leucine zipper consist of a stretch of amino acids with a leucine residue in every seventh position Two proteins form a dimer because they interact by means of leucine zippers on similar α-helical domain. This positions their DNA binding basic domains for interaction with the two halves of a DNA sequence with dyad symmetry of TGACTCA, ACTGAGT.