Mud2 functions in transcription by recruiting the Prp19 and TREX complexes to transcribed genes

The different steps of gene expression are intimately linked to coordinate and regulate this complex process. During transcription, numerous RNA-binding proteins are already loaded onto the nascent mRNA and package the mRNA into a messenger ribonucleoprotein particle (mRNP). These RNA-binding proteins are often also involved in other steps of gene expression than mRNA packaging. For example, TREX functions in transcription, mRNP packaging and nuclear mRNA export. Previously, we showed that the Prp19 splicing complex (Prp19C) is needed for efficient transcription as well as TREX occupancy at transcribed genes. Here, we show that the splicing factor Mud2 interacts with Prp19C and is needed for Prp19C occupancy at transcribed genes in Saccharomyces cerevisiae. Interestingly, Mud2 is not only recruited to intron-containing but also to intronless genes indicating a role in transcription. Indeed, we show for the first time that Mud2 functions in transcription. Furthermore, these functions of Mud2 are likely evolutionarily conserved as Mud2 is also recruited to an intronless gene and interacts with Prp19C in Drosophila melanogaster. Taken together, we classify Mud2 as a novel transcription factor that is necessary for the recruitment of mRNA-binding proteins to the transcription machinery. Thus, Mud2 is a multifunctional protein important for transcription, splicing and most likely also mRNP packaging

Multifunctional factor ENY2 is associated with the THO complex and promotes its recruitment onto nascent mRNA

Metazoan E(y)2/ENY2 is a multifunctional protein important for transcription activation and mRNA export, being a component of SAGA/TFTC and the mRNA export complex AMEX. Here, we show that ENY2 in Drosophila is also stably associated with THO, the complex involved in mRNP biogenesis. The ENY2–THO complex is required for normal Drosophila development, functioning independently on SAGA and AMEX. ENY2 and THO arrive on the transcribed region of the hsp70 gene after its activation, and ENY2 plays an important role in THO recruitment. ENY2 and THO show no direct association with elongating RNA polymerase II. Recruitment of ENY2 and THO occurs by their loading onto nascent mRNA, apparently immediately after its synthesis, while the AMEX component Xmas-2 is loaded onto mRNA at a later stage. Knockdown of either ENY2 or THO, but not SAGA or AMEX, affects the processing of the transcript's 3′ end. Thus, ENY2, as a shared subunit of several protein complexes governing the sequential steps of gene expression, plays an important role in the coordination of these steps

Two Isoforms of Drosophila TRF2 Are Involved in Embryonic Development, Premeiotic Chromatin Condensation, and Proper Differentiation of Germ Cells of Both Sexes

The Drosophila TATA box-binding protein (TBP)-related factor 2 (TRF2 or TLF) was shown to control a subset of genes different from that controlled by TBP. Here, we have investigated the structure and functions of the trf2 gene. We demonstrate that it encodes two protein isoforms: the previously described 75-kDa TRF2 and a newly identified 175-kDa version in which the same sequence is preceded by a long N-terminal domain with coiled-coil motifs. Chromatography of Drosophila embryo extracts revealed that the long TRF2 is part of a multiprotein complex also containing ISWI. Both TRF2 forms are detected at the same sites on polytene chromosomes and have the same expression patterns, suggesting that they fulfill similar functions. A study of the manifestations of the trf2 mutation suggests an essential role of TRF2 during embryonic Drosophila development. The trf2 gene is strongly expressed in germ line cells of adult flies. High levels of TRF2 are found in nuclei of primary spermatocytes and trophocytes with intense transcription. In ovaries, TRF2 is present both in actively transcribing nurse cells and in the transcriptionally inactive oocyte nuclei. Moreover, TRF2 is essential for premeiotic chromatin condensation and proper differentiation of germ cells of both sexes

SAGA and a novel Drosophila export complex anchor efficient transcription and mRNA export to NPC

SAGA/TFTC-type multiprotein complexes play important roles in the regulation of transcription. We have investigated the importance of the nuclear positioning of a gene, its transcription and the consequent export of the nascent mRNA. We show that E(y)2 is a subunit of the SAGA/TFTC-type histone acetyl transferase complex in Drosophila and that E(y)2 concentrates at the nuclear periphery. We demonstrate an interaction between E(y)2 and the nuclear pore complex (NPC) and show that SAGA/TFTC also contacts the NPC at the nuclear periphery. E(y)2 forms also a complex with X-linked male sterile 2 (Xmas-2) to regulate mRNA transport both in normal conditions and after heat shock. Importantly, E(y)2 and Xmas-2 knockdown decreases the contact between the heat-shock protein 70 (hsp70) gene loci and the nuclear envelope before and after activation and interferes with transcription. Thus, E(y)2 and Xmas-2 together with SAGA/TFTC function in the anchoring of a subset of transcription sites to the NPCs to achieve efficient transcription and mRNA export