PubMed Health⌕ Search

Biomedical subjects

M N Prioleau

Publications and source records attributed to M N Prioleau.

9 recordsLinked to original sources
PubMed2001

Transitions in histone acetylation reveal boundaries of three separately regulated neighboring loci.

We have studied developmentally regulated patterns of histone acetylation at high resolution across approximately 54 kb of DNA containing three independently regulated but neighboring genetic loci. These include a folate receptor gene, a 16 kb condensed chromatin region, the chicken beta-globin domain and an adjacent olfactory receptor gene. Within these regions the relative levels of acetylation appear to fall into three classes. The condensed chromatin region maintains the lowest acetylation at every developmental stage. Genes that are inactive show similarly low levels, but activation results in a dramatic increase in acetylation. The highest levels of acetylation are seen at regulatory sites upstream of the genes. These patterns imply the action of more than one class of acetylation. Notably, there is a very strong constitutive focus of hyperacetylation at the 5' insulator element separating the globin locus from the folate receptor region, which suggests that this insulator element may harbor a high concentration of histone acetylases.

5' Untranslated Regions↗
PubMed1999

An insulator element and condensed chromatin region separate the chicken beta-globin locus from an independently regulated erythroid-specific folate receptor gene.

We have identified a folate receptor gene upstream of the chicken beta-globin locus and separated from it by a 16 kbp region of silent chromatin. We find that this receptor is expressed only at a stage of erythroid differentiation (CFU-E) preceding the activation of beta-globin genes, consistent with the role of folate receptors in proliferation. This discovery raises the question of how these two loci are regulated during erythropoiesis. Our data suggest that the folate receptor gene and the beta-globin locus are regulated independently. We show that a 3.3 kbp DNA region upstream of the folate receptor gene is sufficient to induce strong expression of a transgene in CFU-E stage cells. We also find that the region between the beta-globin locus and the folate receptor gene is fully methylated and condensed at this stage of differentiation. Its 3' boundary coincides with the 5' beta-globin insulator. We speculate that the 5' beta-globin boundary element might be important for the proper regulation of two adjacent domains activated at two different stages during differentiation.

Amino Acid Sequence↗
PubMed1998

Control of gene expression in Xenopus early development.

We examine the control of gene expression before and through the MBT in Xenopus laevis. The generalized repression of transcription that occurs before the midblastula transition (MBT) is regulated by a dynamic competition between chromatin and transcription complex assembly. Conditions favoring the access of basal factors (TBP) or transactivators can overcome this transcriptional repression. Changes in DNase I hypersensitivity patterns of the chromatin during early development show that it is more accessible to DNase I before the MBT (and by extension to other DNA interacting proteins) than after the MBT. We also show that at the level of genomic domains, organization of the chromatin matrix attachment sites is random before MBT. We propose that these three components, chromatin domain structure, DNA accessibility, and the transcription complex-chromatin dynamic competition, combine to regulate transcription in the embryo before and through the MBT.

Animals↗
PubMed1997

A RNA polymerase III-based two-hybrid system to study RNA polymerase II transcriptional regulators.

In a previous study, we explored the mechanisms of SNR6 gene activation by grafting a heterologous DNA-binding domain, GAL4-(1-147), to various components of the yeast RNA polymerase III transcription system. Here, we demonstrate that a modified SNR6 gene harboring GAL4-binding sites (UAS(G)-SNR6) can be efficiently activated via an intervening, unrelated protein-protein interaction, thus laying the foundations of a RNA polymerase III-based two-hybrid system. In a model system, the interacting proteins recruiting TFIIIC to DNA were PRP21 and PRP9 or PRP21 and PRP11. Mutations affecting the interaction between PRP21 and PRP9, or PRP21 and PRP11 decreased UAS(G)-SNR6 activation level proportionally. RNA polymerase II transcriptional activators, like GAL4, VP16 or p53, fused to GAL4 DNA-binding domain, did not activate the UAS(G)-SNR6 gene. However, GAL4 strongly activated UAS(G)-SNR6 when GAL80, an interacting protein, was fused to TFIIIC. This result indicates that this two-hybrid system can be used to assess the interactions between RNA polymerase II regulatory proteins and their partners.

DNA-Binding Proteins↗
PubMed1997

A functional analysis of p53 during early development of Xenopus laevis.

p53 is a nuclear protein that acts like a tumor suppressor and is involved in regulation of cellular growth. In Xenopus, the p53 protein is highly expressed during oogenesis and is strictly cytoplasmic in the oocyte. We have analysed its participation in DNA replication and transcription during early development, using the egg and oocyte as model-systems. The injection of sperm nuclei into Xenopus eggs is followed by DNA replication and mitotic events. We show that the endogenous p53 enters the nuclei and moves through a series of discrete sub-nuclear loci whose distribution is S-phase specific. A specific peripheral nuclear localization of p53 is observed before entry into S-phase, followed by an internal localization which is strictly dependent on ongoing DNA synthesis. At no stage in the cell cycle, however, did we observe any co-localization with RPA or PCNA, which were used as initiation or elongation markers for DNA replication. We also show that injection into the nucleus of the oocyte of small amounts of either Xenopus or human p53 - less than 10% of the cytoplasmic storage - is sufficient to block RNA polymerase II-dependent transcription from a coinjected TATA-box-containing reporter plasmid. Transcription is rescued by microinjection of the TATA-box binding protein (TBP), suggesting that nuclear exclusion of p53 during oogenesis may be necessary for transcription of maternal genes. These characteristics are discussed in relation to the regulation of nuclear activities during early embryogenesis.

Animals↗
PubMed1995

Programming of a repressed but committed chromatin structure during early development.

The determination of chromatin for transcription during early development as well as the requirement for trans-acting factors during this period has been analysed in Xenopus. Basal transcription is repressed both during oogenesis and after the mid-blastula transition (MBT), and transactivators are required to relieve this repression. In contrast, transactivators cannot overcome the generalized transcriptional repression which occurs in embryos before MBT. However, they do bind to promoters leading to a repressed but preset chromatin structure. Experiments involving the pre-binding of TATA binding protein (TBP) or of the strong transactivator GAL4-VP16 further show that there is no limiting factor before the MBT, and that it is the recruitment and stabilization of the basal transcription machinery and not of transactivators which is repressed during early development. This multi-step process in gene activation, with activation of promoters temporally uncoupled from their commitment, may be of importance in the regulation of early embryonic events by providing molecular signposts for future determinations.

Animals↗
PubMed1994

Competition between chromatin and transcription complex assembly regulates gene expression during early development.

Xenopus early development is characterized by a generalized absence of transcription, which resumes at the midblastula transition (MBT). We analyzed this regulation using a plasmid containing the c-myc promoter that is under the same developmental control when injected into fertilized eggs. We find that the repression of transcription can be relieved simply by preincubating the reporter plasmid with TATA binding protein (TBP). However, the repression of gene activity normally occurring before the MBT soon becomes dominant over this activation independent of cell cycle phases. This inactivation correlates with chromatin assembly, and titration of chromatin components not only relieves repression of TBP-dependent transcription but also permits the establishment of stable transcription during early development. Our data suggest that the large excess of histones represses gene activity during early development through a dynamic competition between chromatin assembly and transcription complex assembly.

Animals↗
PubMed1993

TFIIIC relieves repression of U6 snRNA transcription by chromatin.

The U6 small nuclear (sn)RNA gene (SNR6) from the yeast Saccharomyces cerevisiae is transcribed by RNA polymerase III in vivo. This gene is unusual in having a TATA box at position -30, and an essential B-block element located downstream of the T-rich termination signal. The B block is one of the two intragenic promoter elements of transfer RNA genes that are recognized by transcription factor (TF)IIIC (ref. 4). But accurate in vitro transcription of yeast U6 snRNA gene by PolIII in a purified system requires only TFIIIB components, including the TATA-box binding protein TBP. Here we report that, after nucleosome reconstitution or chromatin assembly, U6 snRNA synthesis becomes dependent on TFIIIC and on the integrity of the B-block element. This observation resolves an apparent paradox between in vitro and in vivo results concerning the necessity of the downstream B-block element and sheds light on a new role of TFIIIC in gene activation.

Animals↗