Linker histone H1 regulates homeostasis of heterochromatin-associated cRNAs.

Chromatin-associated RNAs (cRNAs) are a poorly characterized fraction of cellular RNAs that co-purify with chromatin. Their full complexity and the mechanisms regulating their packaging and chromatin association remain poorly understood. Here, we address these questions in Drosophila.

Lysine 27 dimethylation of Drosophila linker histone dH1 contributes to heterochromatin organization independently of H3K9 methylation.

Post-translational modifications (PTMs) of core histones are important epigenetic determinants that correlate with functional chromatin states. However, despite multiple linker histone H1s PTMs have been identified, little is known about their genomic distribution and contribution to the epigenetic regulation of chromatin. Here, we address this question in Drosophila that encodes a single somatic linker histone, dH1.

The embryonic linker histone dBigH1 alters the functional state of active chromatin.

Linker histones H1 are principal chromatin components, whose contribution to the epigenetic regulation of chromatin structure and function is not fully understood. In metazoa, specific linker histones are expressed in the germline, with female-specific H1s being normally retained in the early-embryo. Embryonic H1s are present while the zygotic genome is transcriptionally silent and they are replaced by somatic variants upon activation, suggesting a contribution to transcriptional silencing.

Linker histone H1 prevents R-loop accumulation and genome instability in heterochromatin.

Linker histone H1 is an important structural component of chromatin that stabilizes the nucleosome and compacts the nucleofilament into higher-order structures. The biology of histone H1 remains, however, poorly understood. Here we show that Drosophila histone H1 (dH1) prevents genome instability as indicated by the increased γH2Av (H2AvS137P) content and the high incidence of DNA breaks and sister-chromatid exchanges observed in dH1-depleted cells.

Histone H1: Lessons from Drosophila.

Eukaryotic genomes are structured in the form of chromatin with the help of a set of five small basic proteins, the histones. Four of them are highly conserved through evolution, form the basic unit of the chromatin, the nucleosome, and have been intensively studied and are well characterized. The fifth histone, histone H1, adds to this basic structure through its interaction at the entry/exit site of DNA in the nucleosome and makes an essential contribution to the higher order folding of the chromatin fiber.

The Drosophila histone demethylase dKDM5/LID regulates hematopoietic development.

dKDM5/LID regulates transcription of essential developmental genes and, thus, is required for different developmental processes. Here, we report the essential contribution of dKDM5/LID to hematopoiesis in Drosophila. Our results show that dKDM5/LID is abundant in hemocytes and that its depletion induces over-proliferation and differentiation defects of larval hemocytes and disrupts organization of the actin cytoskeleton.

New insights for Drosophila GAGA factor in larvae.

GAGA factor plays important roles during Drosophila embryogenesis and its maternal contribution is essential for early development. Here, the role of GAGA factor was studied in 3rd instar larvae using depletion and overexpression conditions in wing disc and transcriptome analysis. We found that genes changing expression were different to those previously described using GAGA mutants in embryos.

GAGA factor repression of transcription is a rare event but the negative regulation of Trl is conserved in Drosophila species.

GAGA is a highly conserved Drosophila transcription factor encoded by the Trithorax-like (Trl) gene. While GAGA usually activates transcription, it represses its own promoter. Here we show that GAGA-mediated repression of Trl is conserved between two distant Drosophila species.

Combined bottom-up and top-down mass spectrometry analyses of the pattern of post-translational modifications of Drosophila melanogaster linker histone H1.

Linker histone H1 is a major chromatin component that binds internucleosomal DNA and mediates the folding of nucleosomes into a higher-order structure, namely the 30-nm chromatin fiber. Multiple post-translational modifications (PTMs) of core histones H2A, H2B, H3 and H4 have been identified and their important contribution to the regulation of chromatin structure and function is firmly established. In contrast, little is known about histone H1 modifications and their function.

Drosophila melanogaster linker histone dH1 is required for transposon silencing and to preserve genome integrity.

Histone H1 is an intrinsic component of chromatin, whose important contribution to chromatin structure is well-established in vitro. Little is known, however, about its functional roles in vivo. Here, we have addressed this question in Drosophila, a model system offering many advantages since it contains a single dH1 variant.

The structure of a transcription activation subcomplex reveals how σ(70) is recruited to PhoB promoters.

PhoB is a two-component response regulator that activates transcription by interacting with the σ(70) subunit of the E. coli RNA polymerase in promoters in which the -35 σ(70)-recognition element is replaced by the pho box. The crystal structure of a transcription initiation subcomplex that includes the σ(4) domain of σ(70) fused with the RNA polymerase β subunit flap tip helix, the PhoB effector domain and the pho box DNA reveals how σ(4) recognizes the upstream pho box repeat.

New aminoacyl-tRNA synthetase-like protein in insecta with an essential mitochondrial function.

Aminoacyl-tRNA synthetases (ARS) are modular enzymes that aminoacylate transfer RNAs (tRNA) for their use by the ribosome during protein synthesis. ARS are essential and universal components of the genetic code that were almost completely established before the appearance of the last common ancestor of all living species. This long evolutionary history explains the growing number of functions being discovered for ARS, and for ARS homologues, beyond their canonical role in gene translation.

Acetylation of GAGA factor modulates its interaction with DNA.

GAGA is a Drosophila transcription factor that shows a high degree of post-translational modification. Here, we show that GAGA factor is acetylated in vivo. Lysine residues K325 and K373 on basic regions BR1 and BR3 of the DNA binding domain, respectively, are shown to be acetylated by PCAF.

Activation properties of GAGA transcription factor.

GAGA is a Drosophila transcription factor that has been involved in many nuclear activities. We present evidence that GAGA factor enhances transcription by stabilizing pre-initiation complex (PIC) and promoting reinitiation. Formation of PIC prior to GAGA addition prevents activation suggesting that GAGA is required early in the formation of activated complexes.

General, negative feedback mechanism for regulation of Trithorax-like gene expression in vivo: new roles for GAGA factor in flies.

Expression of every gene is first regulated at the transcriptional level. While some genes show acute and discrete periods of expression others show a rather steady expression level throughout development. An example of the latter is Trithorax-like (Trl) a member of the Trithorax group that encodes GAGA factor in Drosophila.

Sterol regulatory element-binding protein-2 negatively regulates low density lipoprotein receptor-related protein transcription.

Low density lipoprotein receptor-related protein (LRP1) binds aggregated LDL (agLDL) leading to a high intracellular cholesteryl ester (CE) accumulation. AgLDL up-regulates LRP1 expression concomitantly with an LDL receptor (LDLR) and sterol regulatory element binding protein (SREBP-2) down-regulation. The objectives were to investigate whether SREBP-2 regulates LRP1 transcription and determine the molecular mechanisms involved in the process.

CCAAT/enhancer binding protein-mediated role of thyroid hormone in the developmental expression of the kidney androgen-regulated protein gene in proximal convoluted tubules.

The kidney androgen-regulated protein (KAP) gene is exclusively expressed in proximal tubules of mouse kidney and in the uterus of pregnant females before they give birth. It displays an exquisite and differential regulation of expression by steroid and thyroid hormones (THs) in different proximal tubule segments. Whereas the pars recta (PR cells) responds to thyroid and sexual hormones, the pars convoluta (PCT cells) represents a truly androgen-dependent compartment because expression occurs only in the presence of androgens and functional androgen receptors.

The GAGA protein of Drosophila is phosphorylated by CK2.

The GAGA factor of Drosophila is a sequence-specific DNA-binding protein that contributes to multiple processes from the regulation of gene expression to the structural organisation of heterochromatin and chromatin remodelling. GAGA is known to interact with various other proteins (tramtrack, pipsqueak, batman and dSAP18) and protein complexes (PRC1, NURF and FACT). GAGA functions are likely regulated at the level of post-translational modifications.

Repression by TTK69 of GAGA-mediated activation occurs in the absence of TTK69 binding to DNA and solely requires the contribution of the POZ/BTB domain of TTK69.

tramtrack 69 (TTK69) is known to repress GAGA-mediated activation of the eve promoter in S2 cells. Here, we show that repression by TTK69 occurs in the absence of bona fide TTK69-binding sites on the template, indicating that it does not require the binding of TTK69 to DNA. Consistent with this interpretation, the POZ/BTB domain of TTK69, which does not bind DNA, is sufficient for repression.

The Drosophila transcription factor tramtrack (TTK) interacts with Trithorax-like (GAGA) and represses GAGA-mediated activation.

In this study, we report the interaction of the Drosophila transcription factors Trithorax-like (GAGA) and tramtrack (TTK). This interaction is documented both in vitro, through GST pull-down assays, as well as in vivo, in yeast and Schneider S2 cells. GAGA and TTK share in common the presence of an N-terminal POZ/BTB domain that was found to be necessary and sufficient for GAGA-TTK interaction.

HMGB1 interacts with many apparently unrelated proteins by recognizing short amino acid sequences.

The chromatin high mobility group protein 1 (HMGB1) is a very abundant and conserved protein that is structured into two HMG box domains plus a highly acidic C-terminal domain. From the ability to bind DNA nonspecifically and to interact with various proteins, several functions in DNA-related processes have been assigned to HMGB1. Nevertheless, its functional role remains the subject of controversy.

Functional mapping of the GAGA factor assigns its transcriptional activity to the C-terminal glutamine-rich domain.

GAGA is a nuclear protein encoded by the Trithorax-like gene in Drosophila that is expressed in at least two isoforms generated by alternative splicing. By means of its specific interaction with DNA, GAGA has been involved in several nuclear transactions including regulation of gene expression. Here we have studied the GAGA(519) isoform as a transcription factor.

The N-terminal POZ domain of GAGA mediates the formation of oligomers that bind DNA with high affinity and specificity.

The Drosophila GAGA factor self-oligomerizes both in vivo and in vitro. GAGA oligomerization depends on the presence of the N-terminal POZ domain and the formation of dimers, tetramers, and oligomers of high stoichiometry is observed in vitro. GAGA oligomers bind DNA with high affinity and specificity.

High mobility group protein 1 interacts specifically with the core domain of human TATA box-binding protein and interferes with transcription factor IIB within the pre-initiation complex.

The high mobility group (HMG) box domain has defined a family of proteins, mostly transcription factors, that specifically interacts with DNA on the minor groove and sharply bends it. The founding member of the family, HMG1, does not specifically recognize regular B-DNA but is recruited to DNA by interaction with other transcription factors and TATA box-binding protein (TBP). However, conflicting effects of HMG1 on transcription have been reported.