A number of factors integrate gene expression into a system
2Instituto De Biotecnologia Y Biomedicina (Biotecmed), Universitat De Valencia, Spain
3Virology Unit, Department of Experimental and Health Sciences, Universitat Pompeu Fabra, Spain
Gene expression is traditionally subdivided into distinct stages (e.g., mRNA synthesis, translation, decay). I will show that a number of yeast factors that were originally identified as either transcription factors (e.g., Rpb4/7, Sfp1) or mRNA decay factors (DFs) (e.g., the 5’ to 3’ exonuclease Xrn1) function in mRNA synthesis, translation and decay. The DFs shuttle between the nucleus and the cytoplasm by a mechanism involving the Karyopherin Kap120, 2 nuclear localization sequences (NLSs) found in Xrn1 and the decaying RNA (1,2). In the nucleus they stimulate transcription (1,2). During transcription, Xrn1, Rpb4/7 and Sfp1 bind RNA Polymerase II transcripts and accompany them to the cytoplasm (2,3,4) where they mediate translation by virtue of their capacity to bind translation initiation factors (3,5); upon an appropriate signal, these factors execute mRNA decay (1,2,6). Binding of Xrn1 to RNA masks Xrn1 NLS1, thus preventing Xrn1 from returning to the nucleus; only following degradation import occurs (2). Our results show a coordinated control of the three main stages of gene expression by various factors to maintain proper homeostasis of gene expression
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