Replication-dependent histone genes are up-regulated during the G1/S phase transition to meet the requirement for histones to package the newly synthesized DNA. In mammalian cells, this increment is achieved by enhanced transcription and 3′ end processing. The non-polyadenylated histone mRNA 3′ ends are generated by a unique mechanism involving the U7 small ribonucleoprotein (U7 snRNP). By using affinity purification methods to enrich U7 snRNA, we identified FUS/TLS as a novel U7 snRNP interacting protein. Both U7 snRNA and histone transcripts can be precipitated by FUS antibodies predominantly in the S phase of the cell cycle. Moreover, FUS depletion leads to decreased levels of correctly processed histone mRNAs and increased levels of extended transcripts. Interestingly, FUS antibodies also co-immunoprecipitate histone transcriptional activator NPAT and transcriptional repressor hnRNP UL1 in 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. Thus, FUS may serve as a linking factor that positively regulates histone gene transcription and 3′ end processing by interacting with the U7 snRNP and other factors involved in replication-dependent histone gene expression.
BackgroundCore canonical histones are required in the S phase of the cell cycle to pack newly synthetized DNA, therefore the expression of their genes is highly activated during DNA replication. In mammalian cells, this increment is achieved by both enhanced transcription and 3′ end processing. In this paper, we described positive cofactor 4 (PC4) as a protein that contributes to the regulation of replication-dependent histone gene expression.ResultsWe showed that PC4 influences RNA polymerase II recruitment to histone gene loci in a cell cycle-dependent manner. The most important effect was observed in S phase where PC4 knockdown leads to the elevated level of RNA polymerase II on histone genes, which corresponds to the increased total level of those gene transcripts. The opposite effect was caused by PC4 overexpression. Moreover, we found that PC4 has a negative effect on the unique 3′ end processing of histone pre-mRNAs that can be based on the interaction of PC4 with U7 snRNP and CstF64. Interestingly, this effect does not depend on the cell cycle.ConclusionsWe conclude that PC4 might repress RNA polymerase II recruitment and transcription of replication-dependent histone genes in order to maintain the very delicate balance between histone gene expression and DNA synthesis. It guards the cell from excess of histones in S phase. Moreover, PC4 might promote the interaction of cleavage and polyadenylation complex with histone pre-mRNAs, that might impede with the recruitment of histone cleavage complex. This in turn decreases the 3′ end processing efficiency of histone gene transcripts.Electronic supplementary materialThe online version of this article (10.1186/s12867-018-0110-y) contains supplementary material, which is available to authorized users.
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