ognizant Communication Corporation

GENE EXPRESSION

ABSTRACTS
VOLUME 9, NUMBER 1-2, 2000

Gene Expression, Vol. 9, pp. 3-13, 2000
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Phosphorylation in Transcription: The CTD and More

Thilo Riedl and Jean-Marc Egly

Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP 163, 67404 Illkirch Cedex, France

Phosphorylation appears to be one mechanism in the regulation of transcription. Indeed, a multitude of factors involved in distinct steps of transcription, including RNA polymerase II, the general transcription factors, pre-mRNA processing factors, and transcription activators/repressors are phosphoproteins and serve as substrates for multiple kinases. Among these substrates, most attention has been paid in recent years to the phosphorylation of the carboxyl-terminal domain (CTD) of RNA polymerase II and its role in transcription regulation. Kinases responsible for such CTD phosphorylation that are associated with RNA polymerase II at distinct steps of transcription, such as cdk7 and cdk8, also phosphorylate some other components of the transcription machinery in a regulatory manner. These observations enlighten the pivotal role of such kinases in an entangled regulation of transcription by phosphorylation. Summarizing the phosphorylation of various components of the transcription machinery, we point out the variety of steps in transcription that are regulated by such protein modifications, envisioning an interconnection of the several stages of mRNA synthesis by phosphorylation.

Key words: Transcription regulation; Phosphorylation; CTD; GTFs; Transcription activators

Address correspondence to Jean Marc Egly, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP 163, 67404 ILLKIRCH Cedex, France. Tel: (33) 3 88 65 34 47; Fax: (33) 3 88 65 32 01; E-mail: egly@igbmc.u-strasbg.fr




Gene Expression, Vol. 9, pp. 15-28, 2000
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RNA Polymerase III Transcription: Its Control by Tumor Suppressors and Its Deregulation by Transforming Agents

Timothy R. P. Brown, Pamela H. Scott, Torsten Stein, Andrew G. Winter, and Robert J. White

Institute of Biomedical and Life Sciences, Division of Biochemistry and Molecular Biology, Davidson Building, University of Glasgow, Glasgow, G12 8QQ, UK

The level of RNA polymerase (pol) III transcription is tightly linked to the rate of growth; it is low in resting cells and increases following mitogenic stimulation. When mammalian cells begin to proliferate, maximal pol III activity is reached shortly before the G1/S transition; it then remains high throughout S and G2 phases. Recent data suggest that the retinoblastoma protein RB and its relatives p107 and p130 may be largely responsible for this pattern of expression. During G0 and early G1 phase, RB and p130 bind and repress the pol III-specific factor TFIIIB; shortly before S phase they dissociate from TFIIIB, allowing transcription to increase. At the end of interphase, when cells enter mitosis, pol III transcription is again suppressed; this mitotic repression is achieved through direct phosphorylation of TFIIIB. Thus, pol III transcription levels fluctuate as mammalian cells cycle, being high in S and G2 phases and low during mitosis and early G1. In addition to this cyclic regulation, TFIIIB can be bound and repressed by the tumor suppressor p53. Conversely, it is a target for activation by several viruses, including SV40, HBV, and HTLV-1. Some viruses also increase the activity of a second pol III-specific factor called TFIIIC. A large proportion of transformed and tumor cell types express abnormally high levels of pol III products. This may be explained, at least in part, by the very high frequency with which RB and p53 become inactivated during neoplastic transformation; loss of function of these cardinal tumor suppressors may release TFIIIB from key restraints that operate in normal cells.

Key words: Cell cycle; p53; RB; Transformation; Transcription; TFIIIB; pol III

Address correspondence to Robert J. White, Institute of Biomedical and Life Sciences, Division of Biochemistry and Molecular Biology, Davidson Building, University of Glasgow, Glasgow, G12 8QQ, UK. Tel: 0141-330-4628; Fax: 0141-330-4620; E-mail: rwhite@udcf.gla.ac.uk




Gene Expression, Vol. 9, pp. 29-36, 2000
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Insight Into the Tumor Suppressor Function of CBP Through the Viral Oncoprotein Tax

Karen Van Orden and Jennifer K. Nyborg

Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870

CREB binding protein (CBP) is a cellular coactivator protein that regulates essentially all known pathways of gene expression. The transcriptional coactivator properties of CBP are utilized by at least 25 different transcription factors representing nearly all known classes of DNA binding proteins. Once bound to their target genes, these transcription factors are believed to tether CBP to the promoter, leading to activated transcription. CBP functions to stimulate transcription through direct recruitment of the general transcription machinery as well as acetylation of both histone and transcription factor substrates. Recent observations indicate that a critical dosage of CBP is required for normal development and tumor suppression, and that perturbations in CBP concentrations may disrupt cellular homeostasis. Furthermore, there is accumulating evidence that CBP deregulation plays a direct role in hematopoietic malignancies. However, the molecular events linking CBP deregulation and malignant transformation are unclear. Further insight into the function of CBP, and its role as a tumor suppressor, can be gained through recent studies of the human T-cell leukemia virus, type I (HTLV-I) Tax oncoprotein. Tax is known to utilize CBP to stimulate transcription from the viral promoter. However, recent data suggest that as a consequence of the Tax-CBP interaction, many cellular transcription factor pathways may be deregulated. Tax disruption of CBP function may play a key role in transformation of the HTLV-I-infected cell. Thus, Tax derailment of CBP may lend important information about the tumor suppressor properties of CBP and serve as a model for the role of CBP in hematopoietic malignancies.

Key words: CREB binding protein (CBP); Tax oncoprotein; Tumor suppression

Address correspondence to Jennifer K. Nyborg, Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870. Tel: (970) 491-0420; Fax: (970) 491-0494; E-mail: jnyborg@lamar.colostate.edu




Gene Expression, Vol. 9, pp. 37-61, 2000
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Role of Histone Acetylation in the Assembly and Modulation of Chromatin Structures

Anthony T. Annunziato1 and Jeffrey C. Hansen2

1Department of Biology, Boston College, 140 Commonwealth Ave., Chestnut Hill, MA 02467
2Department of Biochemistry, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78284

The acetylation of the core histone N-terminal "tail" domains is now recognized as a highly conserved mechanism for regulating chromatin functional states. The following article examines possible roles of acetylation in two critically important cellular processes: replication-coupled nucleosome assembly, and reversible transitions in chromatin higher order structure. After a description of the acetylation of newly synthesized histones, and of the likely acetyltransferases involved, an overview of histone octamer assembly is presented. Our current understanding of the factors thought to assemble chromatin in vivo is then described. Genetic and biochemical investigations of the function the histone tails, and their acetylation, in nucleosome assembly are detailed, followed by an analysis of the importance of histone deacetylation in the maturation of newly replicated chromatin. In the final section the involvement of the histone tail domains in chromatin higher order structures is addressed, along with the role of histone acetylation in chromatin folding. Suggestions for future research are offered in the concluding remarks.

Key words: Histone; Acetylation; Chromatin; Nucleosome; Assembly; Tails; Structure; Folding

Address correspondence to Anthony T. Annunziato, Department of Biology, Boston College, 140 Commonwealth Ave., Chestnut Hill, MA 02467. Tel: (617) 552-3812; Fax: (617) 552-2011; E-mail: anthony.annunziato@bc.edu




Gene Expression, Vol. 9, pp. 63-75, 2000
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DNA Methylation and Histone Deacetylation in the Control of Gene Expression: Basic Biochemistry to Human Development and Disease

Assam El-Osta and Alan P. Wolffe

Laboratory of Molecular Embryology, National Institute of Child Heath and Human Development, NIH, Bethesda, MD 20892-5431

DNA methylation is a major determinant in the epigenetic silencing of genes. The mechanisms underlying the targeting of DNA methylation and the subsequent repression of transcription are relevant to human development and disease, as well as for attempts at somatic gene therapy. The success of transgenic technologies in plants and animals is also compromised by DNA methylation-dependent silencing pathways. Recent biochemical experiments provide a mechanistic foundation for understanding the influence of DNA methylation on transcription. The DNA methyltransferase Dnmt1, and several methyl-CpG binding proteins, MeCP2, MBD2, and MBD3, all associate with histone deacetylase. These observations firmly connect DNA methylation with chromatin modifications. They also provide new pathways for the potential targeting of DNA methylation to repressive chromatin as well as the assembly of repressive chromatin on methylated DNA. Here we discuss the implications of the methylation-acetylation connection for human cancers and the developmental syndromes Fragile X and Rett, which involve a mistargeting of DNA methylation-dependent repression.

Key words: Rett syndrome; Fragile X syndrome; Methyl-CpG binding proteins; DNA methyltransferase; Histone deacetylase; Chromatin remodeling; p161NK4; 5-aza 2´deoxycytidine

Address correspondence to Alan P. Wolffe at his current address: Sangamo Biosciences, 501 Canal Boulevard, suite A100, Richmond, CA 94804. Tel: (510) 970-6000; Fax: (510) 236-8951; E-mail: awolffe@sangamo.com




Gene Expression, Vol. 9, pp. 77-92, 2000
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Chemical Approaches to Control Gene Expression

Joel M. Gottesfeld,1 James M. Turner,1 and Peter B. Dervan2

1Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037
2Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125

A current goal in molecular medicine is the development of new strategies to interfere with gene expression in living cells in the hope that novel therapies for human disease will result from these efforts. This review focuses on small-molecule or chemical approaches to manipulate gene expression by modulating either transcription of messenger RNA-coding genes or protein translation. The molecules under study include natural products, designed ligands, and compounds identified through functional screens of combinatorial libraries. The cellular targets for these molecules include DNA, messenger RNA, and the protein components of the transcription, RNA processing, and translational machinery. Studies with model systems have shown promise in the inhibition of both cellular and viral gene transcription and mRNA utilization. Moreover, strategies for both repression and activation of gene transcription have been described. These studies offer promise for treatment of diseases of pathogenic (viral, bacterial, etc.) and cellular origin (cancer, genetic diseases, etc.).

Key words: Gene transcription; Molecular medicine; Novel therapies; Therapeutic strategies

Address correspondence to Joel M. Gottesfeld, Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037. Tel: (858) 784-8913; Fax: (858) 784-8965; E-mail: joelg@scripps.edu