Cell. different phases of the cell cycle. We further show that FUS binds to histone genes in S phase, promotes the recruitment of RNA polymerase II and is important for the activity of histone gene promoters. Therefore, FUS may serve as a linking element that positively regulates histone gene transcription and 3 end processing by interacting with the U7 snRNP MSK1 and additional factors involved in replication-dependent histone gene manifestation. INTRODUCTION The manifestation of the metazoan replication-dependent histone genes is definitely cell cycle-regulated to meet the requirement for histones to package the newly synthesized DNA during the S phase of the cell cycle. Histone mRNA levels increase 35-collapse during the G1/S phase transition and rapidly drop again at the end of S phase (1,2). The general transcription element NPAT is known to bind to replication-dependent histone gene promoters and to activate transcription during S phase (3), resulting in a 5-fold increase in histone gene transcription (2). Moreover, the S phase-dependent increment of replication-dependent histone mRNAs is also due to more efficient histone RNA 3 end processing. In contrast, the drop in histone mRNA levels in the S/G2 transition is mostly due to a rapid destabilization of the existing mRNAs (2). Replication-dependent histone transcripts are not processed in the 3 end by cleavage coupled to polyadenylation like the majority of eukaryotic pre-mRNAs. Instead, histone mRNA 3 end processing consists of a solitary cleavage that is carried out from the endonuclease CPSF73 and mediated by a subset of specialized factors that identify specific elements within the nascent transcripts (4C6). Histone pre-mRNAs end in a conserved stem loop acknowledged and bound from I-CBP112 the hairpin- or stem loop-binding protein (HBP/SLBP) that defines the cleavage site a few nucleotides downstream, usually after a CA dinucleotide (4,7C8). The additional determinant of the cleavage site is the U7 small ribonucleoprotein (U7 snRNP) that binds by basepairing of the 5 end of U7 snRNA to the histone downstream element (HDE) located 3 of the cleavage site (9,10). The U7 snRNP consists of an approximately 60-nucleotide U7 snRNA (11C13) and an unusual ring of Sm/Lsm proteins in which the two I-CBP112 spliceosomal proteins SmD1 and SmD2 are replaced from the Sm-like proteins Lsm10 and Lsm11 (14,15). Lsm11 consists of an extended N terminus that is necessary for processing and forms a platform for relationships with additional factors. In particular, the U7-specific Lsm11 protein binds to a 100 kDa zinc-finger protein (ZFP100) which in turn interacts with SLBP and stabilizes the complex (16C18). Lsm11 also binds to another histone-specific control element, FLASH (19C21) and to the 68 kDa subunit of mammalian cleavage element I (22). Collectively, the U7 snRNP-specific protein Lsm11 and Adobe flash form a binding platform to recruit a heat-labile processing element (HLF) that contains symplekin, CstF64 and additional components of cleavage/polyadenylation machinery, including the endonuclease CPSF73 (1,21,23C25). Two of the histone processing factors are known to be cell cycle-regulated. These are SLBP (26) and the HLF through its CstF64 subunit (1,25). Moreover, the U7 snRNP offers been shown to play an additional regulatory role. Together with the hnRNP protein UL1, it functions to repress histone gene transcription outside of S phase (27). By using different affinity I-CBP112 purification strategies for U7 snRNA, we have now recognized fused in sarcoma/translocated in liposarcoma (FUS/TLS; named FUS thereafter) as a I-CBP112 new element involved in replication-dependent histone gene manifestation. FUS belongs to the FET family which includes three highly conserved, abundant and ubiquitously indicated RNA-binding proteins: FUS, EWS and TAF15 (28). FUS is definitely predominantly present in the nuclear matrix, although it is definitely also found in cytoplasmic fractions and is supposed to participate in I-CBP112 nucleo-cytoplasmic shuttling (29). FUS binds to both ssDNA and dsDNA and is able to promote DNA annealing and D-loop formation which implies a role in genomic maintenance, DNA recombination and the DNA restoration pathway (30C32). FUS is also capable of binding RNA both in the nucleus and cytoplasm, and thus.