Multiple mixed lineage leukemia (MLL) fusion proteins suppress p53-mediated response to DNA damage.

Chromosomal translocations involving the mixed lineage leukemia (MLL) gene are often observed in acute leukemias of both myeloid and lymphocytic origin. Expression of MLL fusion proteins is known to induce malignant transformation of normal blood progenitors; however, molecular mechanisms of this process are still poorly understood. In this study we investigated the effect of several frequently detected MLL fusion proteins on p53 transcriptional activity.

A COMPASS in the voyage of defining the role of trithorax/MLL-containing complexes: linking leukemogensis to covalent modifications of chromatin.

Chromosomal rearrangements and translocations play a major role in the pathogenesis of hematological malignancies. The trithorax-related mixed lineage leukemia (Mll) gene located on chromosome 11 is rearranged in a variety of aggressive human B and T lymphoid tumors as well as acute myeloid leukemia (AML) in both children and adults. It was first demonstrated for the yeast MLL homolog complex, Set1/COMPASS, and now for the MLL complex itself, that these complexes are histone methyltransferases capable of methylating the fourth lysine of histone H3.

Maintenance of low histone ubiquitylation by Ubp10 correlates with telomere-proximal Sir2 association and gene silencing.

Low levels of histone covalent modifications are associated with gene silencing at telomeres and other regions in the yeast S. cerevisiae. Although the histone deacetylase Sir2 maintains low acetylation, mechanisms responsible for low H2B ubiquitylation and low H3 methylation are unknown.

Regulation of heat shock gene expression by RNA polymerase II elongation factor, Elongin A.

The elongation stage of transcription by RNA polymerase II (Pol II) has emerged as an essential regulated step. Elongin A (EloA) is the largest subunit of the Elongin complex that can increase the catalytic rate of mRNA synthesis by Pol II. We recently demonstrated that the Elongin A homologue in Drosophila, dEloA, is essential and has properties consistent with those of a Pol II elongation factor in vivo.

In vivo requirement of the RNA polymerase II elongation factor elongin A for proper gene expression and development.

A number of transcription factors that increase the catalytic rate of mRNA synthesis by RNA polymerase II (Pol II) have been purified from higher eukaryotes. Among these are the ELL family, DSIF, and the heterotrimeric elongin complex. Elongin A, the largest subunit of the elongin complex, is the transcriptionally active subunit, while the smaller elongin B and C subunits appear to act as regulatory subunits.

Transcriptional elongation control by RNA polymerase II: a new frontier.

The transcription elongation complex, once thought to be composed of merely the DNA template, RNA polymerase II and the nascent RNA transcript, is now burgeoning as a unit as multifaceted and complicated as the transcription initiation complex. Studies concentrated in defining the elongation stage of transcription during the past recent years have resulted in the discovery of a diverse collection of transcription elongation factors that are either directly involved in the regulation of the rate of the elongating RNA polymerase II or can modulate messenger RNA (mRNA) processing and transport. Such studies have demonstrated that the elongation stage of transcription is highly regulated and has opened a new era of studies defining the molecular role of such transcription elongation factors in cellular development, differentiation and disease progression.

Transcriptional activation via sequential histone H2B ubiquitylation and deubiquitylation, mediated by SAGA-associated Ubp8.

Gene activation and repression regulated by acetylation and deacetylation represent a paradigm for the function of histone modifications. We provide evidence that, in contrast, histone H2B monoubiquitylation and its deubiquitylation are both involved in gene activation. Substitution of the H2B ubiquitylation site at Lys 123 (K123) lowered transcription of certain genes regulated by the acetylation complex SAGA.

The Paf1 complex is essential for histone monoubiquitination by the Rad6-Bre1 complex, which signals for histone methylation by COMPASS and Dot1p.

Monoubiquitination of histone H2B, catalyzed by Rad6-Bre1, is required for methylation of histone H3 on lysines 4 and 79, catalyzed by the Set1-containing complex COMPASS and Dot1p, respectively. The Paf1 protein complex, which associates with RNA polymerase II, is known to be required for these histone H3 methylation events. During the early elongation stage of transcription, the Paf1 complex is required for association of COMPASS with RNA polymerase II, but the role the Paf1 complex plays at the promoter has not been clear.

Molecular basis of p53 functional inactivation by the leukemic protein MLL-ELL.

The Eleven Lysine-rich Leukemia (ELL) gene undergoes translocation and fuses in frame to the Multiple Lineage Leukemia (MLL) gene in a substantial proportion of patients suffering from acute forms of leukemia. Molecular mechanisms of cellular transformation by the MLL-ELL fusion are not well understood. Although both MLL-ELL and wild-type ELL can reduce functional activity of p53 tumor suppressor, our data reveal that MLL-ELL is a much more efficient inhibitor of p53 than is wild-type ELL.

Methylation of histone H3 by Set2 in Saccharomyces cerevisiae is linked to transcriptional elongation by RNA polymerase II.

Set2 methylates Lys36 of histone H3. We show here that yeast Set2 copurifies with RNA polymerase II (RNAPII). Chromatin immunoprecipitation analyses demonstrated that Set2 and histone H3 Lys36 methylation are associated with the coding regions of several genes that were tested and correlate with active transcription.

Transcriptional elongation by RNA polymerase II and histone methylation.

mRNA synthesis in eukaryotic organisms is a key biological process that is regulated at multiple levels. From the covalent modifications of chromatin by a number of chromatin remodeling complexes during the initiation and activation steps of transcription to the processing of mRNA transcripts, a very large consortium of proteins and multiprotein complexes is critical for gene expression by RNA polymerase II. The list of proteins essential for the successful synthesis of mRNA continues to grow at a rapid pace.

The RNA polymerase II elongation complex.

Synthesis of eukaryotic mRNA by RNA polymerase II is an elaborate biochemical process that requires the concerted action of a large set of transcription factors. RNA polymerase II transcription proceeds through multiple stages designated preinitiation, initiation, and elongation. Historically, studies of the elongation stage of eukaryotic mRNA synthesis have lagged behind studies of the preinitiation and initiation stages; however, in recent years, efforts to elucidate the mechanisms governing elongation have led to the discovery of a diverse collection of transcription factors that directly regulate the activity of elongating RNA polymerase II.

The Paf1 complex is required for histone H3 methylation by COMPASS and Dot1p: linking transcriptional elongation to histone methylation.

Methylation of histone proteins is one of their many modifications that affect chromatin structure and regulate gene expression. Methylation of histone H3 on lysines 4 and 79, catalyzed by the Set1-containing complex COMPASS and Dot1p, respectively, is required for silencing of expression of genes located near chromosome telomeres in yeast. We report that the Paf1 protein complex, which is associated with the elongating RNA polymerase II, is required for methylation of lysines 4 and 79 of histone H3 and for silencing of expression of a telomere-associated gene.

Bre1, an E3 ubiquitin ligase required for recruitment and substrate selection of Rad6 at a promoter.

Ubiquitination of histone H2B catalyzed by Rad6 is required for methylation of histone H3 by COMPASS. We identified Bre1 as the probable E3 for Rad6's role in transcription. Bre1 contains a C3HC4 (RING) finger and is present with Rad6 in a complex.

RNA polymerase II elongation factors of Saccharomyces cerevisiae: a targeted proteomics approach.

To physically characterize the web of interactions connecting the Saccharomyces cerevisiae proteins suspected to be RNA polymerase II (RNAPII) elongation factors, subunits of Spt4/Spt5 and Spt16/Pob3 (corresponding to human DSIF and FACT), Spt6, TFIIF (Tfg1, -2, and -3), TFIIS, Rtf1, and Elongator (Elp1, -2, -3, -4, -5, and -6) were affinity purified under conditions designed to minimize loss of associated polypeptides and then identified by mass spectrometry. Spt16/Pob3 was discovered to associate with three distinct complexes: histones; Chd1/casein kinase II (CKII); and Rtf1, Paf1, Ctr9, Cdc73, and a previously uncharacterized protein, Leo1. Rtf1 and Chd1 have previously been implicated in the control of elongation, and the sensitivity to 6-azauracil of strains lacking Paf1, Cdc73, or Leo1 suggested that these proteins are involved in elongation by RNAPII as well.

dELL is an essential RNA polymerase II elongation factor with a general role in development.

Several eukaryotic proteins increase RNA polymerase II (Pol II) transcription rates in vitro. The relative contributions of these factors to gene expression in vivo is unknown. The ELL family of proteins promote Pol II elongation in vitro, and the Drosophila ELL homolog (dELL) is associated with Pol II at sites of transcription in vivo.

Methylation of histone H3 by COMPASS requires ubiquitination of histone H2B by Rad6.

The DNA of eukaryotes is wrapped around nucleosomes and packaged into chromatin. Covalent modifications of the histone proteins that comprise the nucleosome alter chromatin structure and have major effects on gene expression. Methylation of lysine 4 of histone H3 by COMPASS is required for silencing of genes located near chromosome telomeres and within the rDNA (Krogan, N.

COMPASS, a histone H3 (Lysine 4) methyltransferase required for telomeric silencing of gene expression.

The trithorax (Trx) family of proteins is required for maintaining a specific pattern of gene expression in some organisms. Recently we reported the isolation and characterization of COMPASS, a multiprotein complex that includes the Trx-related protein Set1 of the yeast Saccharomyces cerevisiae. Here we report that COMPASS catalyzes methylation of the fourth lysine of histone H3 in vitro.

Drosophila ELL is associated with actively elongating RNA polymerase II on transcriptionally active sites in vivo.

Several factors have been biochemically characterized based on their ability to increase the overall rate of transcription elongation catalyzed by the multiprotein complex RNA polymerase II (Pol II). Among these, the ELL family of elongation factors has been shown to increase the catalytic rate of transcription elongation in vitro by suppressing transient pausing. Several fundamental biological aspects of this class of elongation factors are not known.

COMPASS: a complex of proteins associated with a trithorax-related SET domain protein.

The trithorax genes encode an evolutionarily conserved family of proteins that function to maintain specific patterns of gene expression throughout cellular development. Members of this protein family contain a highly conserved 130- to 140-amino acid motif termed the SET domain. We report the purification and molecular identification of the subunits of a protein complex in the yeast Saccharomyces cerevisiae that includes the trithorax-related protein Set1.

Muf1, a novel Elongin BC-interacting leucine-rich repeat protein that can assemble with Cul5 and Rbx1 to reconstitute a ubiquitin ligase.

The heterodimeric Elongin BC complex has been shown to interact in vitro and in mammalian cells with a conserved BC-box motif found in a growing number of proteins including RNA polymerase II elongation factor Elongin A, SOCS-box proteins, and the von Hippel-Lindau (VHL) tumor suppressor protein. Recently, the VHL-Elongin BC complex was found to interact with a module composed of Cullin family member Cul2 and RING-H2 finger protein Rbx1 to reconstitute a novel E3 ubiquitin ligase that activates ubiquitylation by the E2 ubiquitin-conjugating enzymes Ubc5 and Cdc34. In the context of the VHL ubiquitin ligase, Elongin BC functions as an adaptor that links the VHL protein to the Cul2/Rbx1 module, raising the possibility that the Elongin BC complex could function as an integral component of a larger family of E3 ubiquitin ligases by linking alternative BC-box proteins to Cullin/Rbx1 modules.

Cloning and characterization of ELL-associated proteins EAP45 and EAP20. a role for yeast EAP-like proteins in regulation of gene expression by glucose.

RNA polymerase II elongation factor ELL was recently purified from rat liver as a component of a multiprotein complex containing ELL and three ELL-associated proteins (EAPs) of approximately 45 (EAP45), approximately 30 (EAP30), and approximately 20 (EAP20) kDa (Shilatifard, A. (1998) J. Biol.