title: Translation regulation and proteasome mediated degradation cooperate to keep stem-loop binding protein low in G1-phase.
abstract: Histone mRNA levels are cell cycle regulated, and the major regulatory steps are at the posttranscriptional level. A major regulatory mechanism is S-phase restriction of Stem-loop binding protein (SLBP) which binds to the 3' end of histone mRNA and participates in multiple steps of histone mRNA metabolism, including 3' end processing, translation and regulation of mRNA stability. SLBP expression is cell cycle regulated without significant change in its mRNA level. SLBP expression is low in G1 until just before S phase where it functions and at the end of S phase SLBP is degraded by proteasome complex depending on phosphorylations on Thr60 and Thr61. Here using synchronized HeLa cells we showed that SLBP production rate is low in early G1 and recovers back to S phase level somewhere between early and mid-G1. Further, we showed that SLBP is unstable in G1 due to proteasome mediated degradation as a novel mechanism to keep SLBP low in G1. Finally, the S/G2 stable mutant form of SLBP is degraded by proteasome in G1, indicating that indicating that the SLBP degradation in G1 is independent of the previously identified SLBP degradation at S/G2. In conclusion, as a mechanism to limit histone production to S phase, SLBP is kept low in G1 phase due to cooperative action of translation regulation and proteasome mediated degradation which is independent of previously known S/G2 degradation.
authors.affiliation: Department of Genetics and Bioengineering, Fatih University Istanbul, Istanbul, Turkey; Bionanotechnology Center, Fatih University Istanbul, Istanbul, Turkey.
authors.forename: Umidahan
authors.initials: U
authors.lastname: Djakbarova
authors.forename: William F
authors.initials: WF
authors.lastname: Marzluff
authors.forename: M Murat
authors.initials: MM
authors.lastname: Köseoğlu
mesh_terms: D016193:G1 Phase / Q000235:genetics; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D014176:Protein Biosynthesis; D059748:Proteolysis; D012333:RNA, Messenger / Q000235:genetics; D039221:mRNA Cleavage and Polyadenylation Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D006657:Histones; D009687:Nuclear Proteins; D012333:RNA, Messenger; C092663:SLBP protein, human; D039221:mRNA Cleavage and Polyadenylation Factors; D046988:Proteasome Endopeptidase Complex
keywords: HISTONE SYNTHESIS; HISTONE mRNA; REPLICATION DEPENDENT HISTONE GENES; SLBP