[The SAGA Deubiquitinilation (DUB) Module Participates in Pol III-Dependent Transcription].

SAGA, the multicomponent complex responsible for acetylation of histone N-terminal lysine residues, is involved in the transcription activation of a wide range of eukaryote genes. SAGA contains a protein module, DUB, which is responsible for histone deubiquitination. In this paper we show that the DUB module may be found within cells independently of SAGA. In the absence of" SAGA, the DUB module may be recruited to the promoters of Pol III-transcribed genes, but not to the Pol II-dependent promoters. The DUB module is required to recruit transcription factor Brfl, a subunit of the Pol III-recruiting TFIIIB complex, to the promoters of Pol III-dependent genes. The DUB-module interacts with Pol III in vivo. The DUB-module is essential for recruiting both TFIIIB complexes and PBP complexes to the promoters of Pol III-dependent genes.

PCID2, a subunit of the Drosophila TREX-2 nuclear export complex, is essential for both mRNA nuclear export and its subsequent cytoplasmic trafficking.

The TREX-2 complex is essential for the general nuclear mRNA export in eukaryotes. TREX-2 interacts with the nuclear pore and transcriptional apparatus and links transcription to the mRNA export. However, it remains poorly understood how the TREX-2-dependent nuclear export is connected to the subsequent stages of mRNA trafficking. Here, we show that the PCID2 subunit of Drosophila TREX-2 is present in the cytoplasm of the cell. The cytoplasmic PCID2 directly interacts with the NudC protein and this interaction maintains its stability in the cytoplasm. Moreover, PCID2 is associated with the cytoplasmic mRNA and microtubules. The PCID2 knockdown blocks nuclear export of mRNA and also affects the general mRNA transport into the cytoplasm. These data suggest that PCID2 could be the link between the nuclear TREX-2-dependent export and the subsequent cytoplasmic trafficking of mRNA.

The Xmas-2 Homologues, the Main Component of the TREX-2 mRNA Export Complex.

TREX-2 complex is responsible for general mRNA export from nucleus to cytoplasm in eukaryote. The main protein of TREX-2 complex of D. melanogaster is protein Xmas-2. Its homologues in yeast and humans are Sac3 and GANP proteins, respectively. All three proteins contain the highly conserved domain Sac3-GANP, which is essential for interaction of TREX-2 complex with mRNA and another protein of the complex, PCID2. We identified two Xmas-2 homologues in D. melanogaster using the Sac3-GANP family domain sequence. These proteins have a common domain responsible for interaction with the PCID2 protein and RNA and are present in other eukaryotes. The function of these proteins is unknown. However, on the basis of their structural organization, we can assume that they interact with nucleic acids.

The role of SAGA coactivator complex in snRNA transcription.

The general snRNA gene transcription apparatus has been extensively studied. However, the role of coactivators in this process is far from being clearly understood. Here, we have demonstrated that the Drosophila SAGA complex interacts with the PBP complex, the key component of the snRNA gene transcription apparatus, and is present at the promoter regions of the snRNA genes transcribed by both the RNA polymerase II and RNA polymerase III (U6 snRNA). We show that SAGA interacts with the Brf1 transcription factor, which is a part of the RNA polymerase III transcription apparatus and is present at promoters of a number of Pol III-transcribed genes. Mutations inactivating several SAGA subunit genes resulted in reduced snRNA levels in adult flies, indicating that SAGA is indeed the transcriptional coactivator for the snRNA genes. The transcription of the Pol II and Pol III-transcribed U genes was reduced by mutations in all tested SAGA complex subunits. Therefore, the transcription of the Pol II and Pol III-transcribed U genes was reduced by the mutations in the deubiquitinase module, as well as in the acetyltransferase module of the SAGA, indicating that the whole complex is essential for their transcription. Therefore, the SAGA complex activates snRNA genes suggesting its wide involvement in the regulation of gene transcription, and consequently, in the maintenance of cellular homeostasis.

Alternative Splicing of the Xmas mRNA Encoding the mRNA Export Protein in Drosophila melanogaster.

It is shown that Drosophila melanogaster has Xmas mRNA whose alternative splicing leads to the formation of three transcripts: Xmas, Xmas-2, and Xmas-1. As a result, three proteins are synthesized: Xmas, Xmas-2, and, presumably, Xmas-1. The size of the Xmas protein is close to the size of its homologue in humans. Adult flies contain large amounts of this protein, whereas in embryos it is absent.

[Activation of JAK/STAT signaling pathway in S2 Drosophila melanogaster cell culture].

JAK/STAT signaling pathway plays a critical role in different ontogenesis processes of higher eukaryotes. Fruit fly drosophila is a handy model system used to study this pathway since major components of the pathway are represented by unique factors. This article describes the usage of Drosophila melanogaster S2 cells in studies of the pathway's target genes activation. We showed that S2 cells contain plenty of STAT protein which migrates into nucleus under cells treatment with pervanadate. Then we demonstrated that under pervanadate action STAT protein along with other transcription factors is recruited onto regulatory sequences of target genes and activates their transcription.

[The role of multifunctional coactivator complex saga in regulation of eukaryotic gene expression].

Eukaryotic gene expression is known as a multistep process of high complexity. Transcription is one of cardinal and tightly regulated phase during gene expression. To provide accurate and precise work of gene regulation apparatus including a plethora of modification of chromatin structure and nucleosome dynamic turnover must be occurred. All transcription steps are under control of large multiprotein coactivator complexes. In this review we discuss an evolutionary conservative SAGA complex, which acetylates and deubiquitinates histones during transcription activation and furthermore is involved in subsequent stages of mRNP biogenesis and export.

[SAGA complex: the role in viability and development].

SAGA is a histone acetyltransferase complex, that cotranscriptionally performs histone modifications and is implicated in regulation of gene expression at the level of changes in chromatin structure. SAGA is also involved in mRNP biogenesis and export. In this review, we examined a contribution of SAGA and its subunits in the development. We also discuss the diseases associated with impaired activity of SAGA subunits.

[SAYP interacts with DHR3 nuclear receptor and participates in ecdysone-dependent transcription regulation].

The role of metazoan coactivator SAYP in nuclear receptor-driven gene activation in the ecdysone cascade of Drosophila is considered. SAYP interacts with DHR3 nuclear receptor and activates the corresponding genes by recruiting the BTFly (Brahma and TFIID) coactivator supercomplex. The knockdown of SAYP leads to a decrease in the level of DHR3-activated transcription. DHR3 and SAYP interact during development and have multiple common targets across the genome.

[Novel conservative domain of SAYP coactivator mediates TFIID and Brahma transcriptional complexes interaction].

In the S2 cell system of Drosophila melanogaster a key protein domain mediating the interaction of TFIID and Brahma transcriptional complexes into the BTFly supercomplex has been shown to be an evolutionary conserved SAY domain of the SAYP. TFIID and Brahma coactivators participated in the reporter gene activation induced by the SAY domain in cellular nuclei. The TFIID and Brahma components directly interacting with the SAY domain were identified.

[SAYP--a novel regulator of metazoan development].

SAYP is a dual-function transcriptional coactivator of RNA polymerase II. It is a metazoan-specific factor involved in different signaling pathways that control normal development. In Drosophila, SAYP is present in the organism from the early stages of development and participates in cell cycle synchronization at the blastoderm stage. SAYP is abundant in many embryonic cells and in imaginal discs of larvae and is crucial for oogenesis in adults. At the molecular level, SAYP serves as a basis for assembling the BTFly nuclear supercomplex consising of the Brahma and TFIID coactivators. We suppose that BTFly and other similar nuclear supercomplexes play an important role in ontogenesis.

[Multifunctional factor ENY2 integrates the various stages of gene expression].

The ENY2/Sus1 is a multifunctional transcription factor which couples transcription with mRNA export. It is the component of the SAGA/TFTC and TREX-2/AMEX protein complexes. Recently, we described the interaction of ENY2 with one more protein complex, THO. Moreover, our data indicate that ENY2 associates with other nuclear and cytoplasmic factors. Thus, being the component of a number of protein complexes, ENY2 plays the role of an adaptor molecule, involved into the integration of different cellular processes, specifically, subsequent stages of gene expression.

[Conservative E(y)2/Sus1 protein is the member of SAGA complex and new nuclear pore-associated complex in Drosophila].

The SGA/TFTC complex plays an important role in the regulation of transcription. We have examined the significance of the gene positioning in the nucleus for its transcription and subsequent export of nascent mRNA. It was demonstrated that E(y)2 protein was a subunit of the SAGA/TFTC histone acetyl transferase complex in Drosophila and that E(y)2 concentrated at the nuclear periphery. An interaction between E(y)2 and the nuclear pore complex (NPC) was demonstrated, as well as that SAGA/TFTC also contacted the NPC at nuclear periphery. In addition, it was shown that E(y)2 formed complex with the Xmas-2 protein (X-linked male sterile 2) both in normal conditions and after heat shock. Importantly, the E(y)2 and Xmas-2 knockdown decreased the contact between the heat-shock protein 70 (hsp70) gene loci and the nuclear envelope before and after activation, and interfered with the transcription. Thus, E(y)2 and Xmas-2 together with SAGA/TFTC functioned in the anchoring of a subset of transcription sites to the NPCs to achieve efficient transcription and mRNA export.

[E(y)2, the novel component of SAGA/TFTC complex in eucaryotes participates in export of mRNP from nucleus and couples transcription with nuclear pore].

For many years transcription was studied independently from the following stages of gene expression. However the tight connection between different stages of gene expression became evident during the last years. This review discusses the new molecular mechanisms coordinating transcription and mRNA export from the nucleus and coupling of transcription and position of the gene in the nucleus. The new protein E(y)2 which plays an important role in these processes is described.

[Conservative E(y)2/Sus1 protein interacts with the Su(Hw)-dependent insulators in Drosophila].

Insulators are regulatory elements having two properties. First, they are able to disturb the interaction between promoters and enhancers/silencers. Second, they are able to block distribution of the heterochromatin. The best-studied are the Su(Hw)-dependent insulators of Drosophila melanogaster, activity of which is determined by the Su(Hw) protein. In this study it was demonstrated that novel, evolutionary conservative transcription factor E(y)2/Sus1 interacted with the Su(Hw) zinc-finger domain and was present in the protein complex, associated with the Su(Hw)-dependent insulators.

[Novel complex, formed by transcription coactivator SAYP].

The multisubunit complex which contains the novel evolutionarily conservative transcription factor SAYP was isolated and the protein composition of the complex was determined. It was shown that SAYP unites two complexes with different functions in transcription activation: the chromatin - remodeling complex PBAP (SWI/SNF) and the main component of preinitiation complex of Pol II, general transcription factor TFIID. The isolated super-complex contained the full set of PBAP and TFIID subunits. All components of supercomplex (SAYP, TFIID and PBAP) are essential for its effective interaction with promoters of SAYP-dependent genes.

[Functions of transcription factor TRF2 in Drosophila melanogaster].

A study was made of the function of the Drosophila melanogaster TRF2 protein. Expression analysis of the trf2(P1) mutation implicated TRF2 in the D. melanogaster embryo development. High-level expression of the trf2 gene was observed in female germline cells. A high level of TRF2 was detected in primary spermatocytes and trophocytes, characterized by intense transcription. In the female gonads, TRF2 was detected in both nurse cells with intense transcription and transcriptionally inactive oocyte nuclei. In addition, TRF2 proved to be necessary for premeiotic chromatin condensation and further differentiation of germline cells.

[Study of the Drosophila melanogaster trf2 gene and its protein product].

The Drosophila melanogaster TRF2 protein regulates transcription of several genes. The trf2 gene structure was studied. The gene proved to code for two protein isoforms, a known 75-kDa isoform and a newly identified 175-kDa isoform. The new isoform combines the known isoform sequence with an extended N end containing a coiled-coil motif. The long TRF2 isoform was found to act as a component of a multiprotein complex, including ISWI ATPase as well.