Biomedical subjects

J C Lucchesi

Publications and source records attributed to J C Lucchesi.

At least 19 recordsLinked to original sources

PubMed2001

Linking global histone acetylation to the transcription enhancement of X-chromosomal genes in Drosophila males.

It has become well established for several genes that targeting of histone acetylation to promoters is required for the activation of transcription. In contrast, global patterns of acetylation have not been ascribed to any particular regulatory function. In Drosophila, a specific modification of H4, acetylation at lysine 16, is enriched at hundreds of sites on the male X chromosome due to the activity of the male-specific lethal (MSL) dosage compensation complex. Utilizing chromatin immunoprecipitation, we have determined that H4Ac16 is present along the entire length of X-linked genes targeted by the MSL complex with relatively modest levels of acetylation at the promoter regions and high levels in the middle and/or 3' end of the transcription units. We propose that global acetylation by the MSL complex increases the expression of X-linked genes by facilitating transcription elongation rather than by enhancing promoter accessibility. We have also determined that H4Ac16 is absent from a region of the X chromosome that includes a gene known to be dosage-compensated by a MSL-independent mechanism. This study represents the first biochemical interpretation of the very large body of cytological observations on the chromosomal distribution of the MSL complex.

Acetylation↗

PubMed2000

The yeast NuA4 and Drosophila MSL complexes contain homologous subunits important for transcription regulation.

In Drosophila, the MSL complex is required for the dosage compensation of X-linked genes in males and contains a histone acetyltransferase, MOF. A point mutation in the MOF acetyl-CoA-binding site results in male-specific lethality. Yeast Esa1p, a MOF homolog, is essential for cell cycle progression and is the catalytic subunit of the NuA4 acetyltransferase complex. Here we report that NuA4 purified from yeast with a point mutation in the acetyl-CoA-binding domain of Esa1p exhibits a strong decrease in histone acetyltransferase activity, yet has no effect on growth. We demonstrate that Eaf3p (Esa1p-associated factor-3 protein), a yeast protein homologous to the Drosophila dosage compensation protein MSL3, is also a stable component of the NuA4 complex. Unlike other subunits of the complex, it is not essential, and the deletion mutant has no growth phenotype. NuA4 purified from the mutant strain has a decreased apparent molecular mass, but retains wild-type levels of histone H4 acetyltransferase activity. The EAF3 deletion and the ESA1 mutation lead to a decrease in PHO5 gene expression; the EAF3 deletion also significantly reduces HIS4 and TRP4 expressions. These results, together with those previously obtained with both the MSL and NuA4 complexes, underscore the importance of targeted histone H4 acetylation for the gene-specific activation of transcription.

Acetyltransferases↗

PubMed2000

Targeting the chromatin-remodeling MSL complex of Drosophila to its sites of action on the X chromosome requires both acetyl transferase and ATPase activities.

Dosage compensation in Drosophila is mediated by a multiprotein, RNA-containing complex that associates with the X chromosome at multiple sites. We have investigated the role that the enzymatic activities of two complex components, the histone acetyltransferase activity of MOF and the ATPase activity of MLE, may have in the targeting and association of the complex with the X chromosome. Here we report that MLE and MOF activities are necessary for complexes to access the various X chromosome sites. The role that histone H4 acetylation plays in this process is supported by our observations that MOF overexpression leads to the ectopic association of the complex with autosomal sites.

Acetylation↗

PubMed2000

A new human member of the MYST family of histone acetyl transferases with high sequence similarity to Drosophila MOF.

We have identified a novel human gene product, hMOF, which exhibits significant similarity to the Drosophila dosage compensation regulator, MOF. A recombinant C-terminal portion of hMOF has histone acetyltransferase activity directed toward histones H3, H2A and H4, a specificity characteristic of other MYST family histone acetyltransferases. Based on hMOF's chromodomain, we discuss possible interactions with other proteins.

Acetyltransferases↗

PubMed2000

Recycling to remodel: evolution of dosage-compensation complexes.

In diploid species where sex determination involves heteromorphic sex chromosomes, a mechanism has evolved to compensate for gene-dosage differences in sex-linked genes between the sexes. This regulatory mechanism, which is based on chromatin remodeling, is the function of complexes that include components themselves involved in other cellular functions or with homologs that are involved in such functions. Directing these complexes to the correct chromosome in the appropriate sex relies on pioneer or novel components as well as on the presence of sequence-dependent target sites.

Animals↗

PubMed2000

The drosophila MSL complex acetylates histone H4 at lysine 16, a chromatin modification linked to dosage compensation.

In Drosophila, dosage compensation-the equalization of most X-linked gene products in males and females-is achieved by a twofold enhancement of the level of transcription of the X chromosome in males relative to each X chromosome in females. A complex consisting of at least five gene products preferentially binds the X chromosome at numerous sites in males and results in a significant increase in the presence of a specific histone isoform, histone 4 acetylated at lysine 16. Recently, RNA transcripts (roX1 and roX2) encoded by two different genes have also been found associated with the X chromosome in males. We have partially purified a complex containing MSL1, -2, and -3, MOF, MLE, and roX2 RNA and demonstrated that it exclusively acetylates H4 at lysine 16 on nucleosomal substrates. These results demonstrate that the MSL complex is responsible for the specific chromatin modification characteristic of the X chromosome in Drosophila males.

Animals↗

PubMed1999

Dosage compensation: roX marks the spot.

The roX genes of Drosophila produce a transcript that is spliced and polyadenylated but not translated. Recent work has shown that these genes provide an element that the dosage compensation complex of Drosophila uses to initiate its association with the X chromosome.

Animals↗

PubMed1999

On the origin of sex chromosomes.

In all living forms, the organization of the genetic material must enable two universally fundamental functions: the elaboration of biological properties and their transmission. In spite of these inexorable commonalties, genomes have a bewildering variety of forms, with differences occurring not only among distant taxa but also, in many instances, between members of the opposite sex within species. The rapidly growing field of comparative genomics offers a powerful tool for unraveling the evolutionary pathways that led to these karyotypic differences. This new method of genetic analysis [Fridolfsson et al, Proc Nat Acad Sci USA 1998; 95: 8147-8152. (Ref. 1)] complements still valuable, traditional experimental approaches.

Animals↗

PubMed1998

ESA1 is a histone acetyltransferase that is essential for growth in yeast.

Posttranslational acetylation of core histone amino termini has long been associated with transcriptionally active chromatin. Recent reports have demonstrated histone acetyltransferase activity in a small group of conserved transcriptional regulators directly linked to gene activation. In addition, the presence of a putative acetyltransferase domain has been discovered in a group of proteins known as the MYST family (for its founding members MOZ, YBF2/SAS3, SAS2, and Tip60). Members of this family are implicated in acute myeloid leukemia (MOZ), transcriptional silencing in yeast (SAS2 and YBF2/SAS3), HIV Tat interaction in humans (Tip60), and dosage compensation in Drosophila (MOF). In this report, we express a yeast ORF with homology to MYST family members and show it possesses histone acetyltransferase activity. Unlike the other MYST family members in Saccharomyces cerevisiae this gene is essential for growth.

Acetyltransferases↗

PubMed1998

Targeting of MOF, a putative histone acetyl transferase, to the X chromosome of Drosophila melanogaster.

Dosage compensation ensures that males with a single X chromosome have the same amount of most X-linked gene products as females with two X chromosomes. In Drosophila, this equalization is achieved by a twofold enhancement of the level of transcription of the X in males relative to each X chromosome in females. The products of at least five genes, maleless (mle), male-specific lethal 1, 2, and 3 (msl-1, msl-2, msl-3) and males absent on the first (mof), are necessary for dosage compensation. The proteins produced by these genes form a complex that is preferentially associated with numerous sites on the X chromosome in somatic cells of males but not of females. Binding of the dosage compensation complex to the X chromosome is correlated with a significant increase in the presence of a specific histone isoform, histone 4 acetylated at lysine 16, on this chromosome. Experimental results and sequence analysis suggest that the mof gene encodes an acetyl transferase that plays a direct role in the specific histone acetylation associated with dosage compensation. Recently, RNA transcripts encoded by at least two different genes have also been found associated with the X chromosome in males. We have studied the role played by the various components of the complex in the targeting of MOF to the X chromosome. To this end, we have used indirect cytoimmunofluorescence to monitor the binding of these components in males carrying complete or partial loss-of-function mutations as well as in XX individuals in which formation of the dosage compensation complex has been induced by genetic means.

Acetyltransferases↗

PubMed1998

Unraveling the role of helicases in transcription.

Proteins with seven conserved "helicase domains" play essential roles in all aspects of nucleic acid metabolism. Deriving energy from ATP hydrolysis, helicases alter the structure of DNA, RNA, or DNA:RNA duplexes, remodeling chromatin and modulating access to the DNA template by the transcriptional machinery. This review focuses on the diverse functions of these proteins in the process of RNA polymerase II transcription in eukaryotes. Known or putative helicases are required for general transcription initiation and for transcription-coupled DNA repair, and may play important roles in elongation, termination, and transcript stability. Recent evidence suggests that helicase-domain-containing proteins are also involved in complexes that facilitate the activity of groups of seemingly unrelated genes.

Animals↗

PubMed1998

Dosage compensation in flies and worms: the ups and downs of X-chromosome regulation.

Dosage compensation ensures that individuals with a single X chromosome have the same amount of most X-linked gene products as those with two. In Drosophila, this equalization is achieved by a two-fold enhancement of the level of transcription of the X in males (XY) relative to each X chromosome in females (XX). In Caenorhabditis, equalization of X-linked gene products between hermaphrodites (XX) and males (XO) is achieved by decreasing the activity of genes in the former. These two different solutions to the common problem of unequal dosage of X-linked genes in different sexes provide invaluable paradigms for the study of gene regulation at the level of chromatin remodeling.

Animals↗

PubMed1997

mof, a putative acetyl transferase gene related to the Tip60 and MOZ human genes and to the SAS genes of yeast, is required for dosage compensation in Drosophila.

Dosage compensation is a regulatory process that insures that males and females have equal amounts of X-chromosome gene products. In Drosophila, this is achieved by a 2-fold enhancement of X-linked gene transcription in males, relative to females. The enhancement of transcription is mediated by the activity of a group of regulatory genes characterized by the male-specific lethality of their loss-of-function alleles. The products of these genes form a complex that is preferentially associated with numerous sites on the X chromosome in somatic cells of males but not of females. Binding of the dosage compensation complex is correlated with a significant increase in the presence of a specific histone isoform, histone 4 acetylated at Lys16, on this chromosome. Experimental results and sequence analysis suggest that an additional gene, males-absent on the first (mof), encodes a putative acetyl transferase that plays a direct role in the specific histone acetylation associated with dosage compensation. The predicted amino acid sequence of MOF exhibits a significant level of similarity to several other proteins, including the human HIV-1 Tat interactive protein Tip60, the human monocytic leukemia zinc finger protein MOZ and the yeast silencing proteins SAS3 and SAS2.

Acetyltransferases↗

PubMed1996

Tosca: a Drosophila gene encoding a nuclease specifically expressed in the female germline.

We describe here a Drosophila gene, tosca (tos), that is specifically expressed in the female germline. tos mRNA accumulates selectively within the pro-oocyte in germarial region 2 and persists throughout oogenesis. In the early embryo, the maternally supplied tos mRNA is evenly distributed at the syncytial blastoderm stage, but is excluded from the forming cells when cellularization begins. tos product is the first Drosophila member of the RAD2 protein family, a group of related DNA repair nucleases conserved from yeast to humans. Within the family, Tos is more closely related to ExoI, a Schizosaccharomyces pombe 5'-->3' double-stranded DNA exonuclease specifically induced in meiotic prophase I. The definite oocyte localization of tos transcript during meiosis and its ubiquitous distribution in early embryos suggest that tos may play a role in mismatch repair during genetic recombination and early cleavage divisions.

Amino Acid Sequence↗

PubMed1996

Dosage compensation in Drosophila and the "complex' world of transcriptional regulation.

The purpose of this review is to draw attention to the mechanism of dosage compensation in Drosophila as a model for the study of the regulation of gene activity through the modulation of transcription. Dosage compensation resembles some mechanisms of transcriptional regulation, found in widely divergent organisms, that do not play a role in the activation of silent genes but determine the level of activity of genes that have been induced through the action of specific activators. It differs from other known regulatory mechanisms in that its effect is to achieve, on average, a twofold change in gene activity levels. This review introduces the notion that, in order to yield such a defined level of regulation, the mechanism of dosage compensation in Drosophila, and perhaps in Caenorhabditis as well, incorporates elements that govern both transcriptional enhancement and repression within the same multi-protein regulatory complex.

Animals↗

PubMed1996

Dosage compensation in Drosophila: the X chromosome binding of MSL-1 and MSL-2 in female embryos is prevented by the early expression of the Sxl gene.

In wildtype males, binding of the MSL-1 gene product to the X chromosome is first seen at the cellular blastoderm stage (stage 5). MSL-2 is associated with the X chromosome in male embryos at a later stage, but the difference in apparent binding time between these two proteins is probably due to a difference in the sensitivity of their respective antisera. Early binding of MSL-1 is never seen in wildtype female embryos, and we have determined that this inhibition is mediated by the SXL product made by the activation of the early Sxl promoter. Once it is allowed to occur, the early X chromosome association of the MSLs is relatively stable, persisting in some cases through the first larval instar in spite of the presence of SXL levels concordant with normal female development. The results of these experiments are discussed in light of their relevance to the established observations that (1) the SXL made by the early promoter inhibits the hypertranscription of run at the blastoderm stage, and (2) severe disturbances in SXL function (loss in XX individuals and gain in haplo-X individuals) result in lethality during embryogenesis while loss of msl function kills males much later.

Animals↗

PubMed1995

The chromo superfamily: new members, duplication of the chromo domain and possible role in delivering transcription regulators to chromatin.

Using computer methods for detecting conserved amino acid sequence motifs, we show that the chromatin organization modifier (chromo) domain that has been previously identified in several proteins involved in transcription down-regulation is present in a much larger group of (putative) chromatin-binding proteins, some of which are positive rather than negative regulators of transcription. The most interesting new members of the chromo superfamily are Drosophila male-specific lethal (MSL-3) protein involved in the X chromosome gene dosage compensation in the males and human retinoblastoma-binding protein RBP-1. We show that the chromo domain is duplicated in several chromatin-binding proteins and use this observation to interpret recent results on chromatin binding obtained with chimeric chromo domain-containing proteins. We hypothesize that the chromo domain may be a vehicle that delivers both positive and negative transcription regulators to the sites of their action on chromatin.

Amino Acid Sequence↗

PubMed1994

Dosage compensation in Drosophila: the X-chromosomal binding of MSL-1 and MLE is dependent on Sxl activity.

In Drosophila, dosage compensation, i.e. the equalization of levels of X-linked gene products in the two sexes, is achieved by the hypertranscription of most X-linked genes in males relative to females. The products of at least four genes, collectively termed male-specific lethal (msl) genes, are required for this process and, at least in the case of three of them, mediate this function through an association with the X chromosome in males. We have studied some of the parameters that affect the association of the msl-1 gene product and found that its presence is dependent on the wild-type function of the other three genes, leading to the conclusion that these gene products contribute to the formation of a multi-subunit complex. Furthermore, the X-chromosomal association of the msl-1 and mle gene products is negatively correlated with the level of function of the master regulatory gene Sxl and can assume either a mosaic or a uniform distribution in the tissues of mutant XX individuals. Surprisingly, we also found that the association of these two msl gene products with the two X chromosomes in females of certain mutant genotypes does not result in the hypertranscription of X-linked genes or in any apparent reduction in viability.

Animals↗