Cdc14 inhibits transcription by RNA polymerase I during anaphase

Abstract

Chromosome condensation and the global repression of gene transcription1 are features of mitosis in most eukaryotes. The logic behind this phenomenon is that chromosome condensation prevents the activity of RNA polymerases. In budding yeast, however, transcription was proposed to be continuous during mitosis2. Here we show that Cdc14, a protein phosphatase required for nucleolar segregation3 and mitotic exit4, inhibits transcription of yeast ribosomal genes (rDNA) during anaphase. The phosphatase activity of Cdc14 is required for RNA polymerase I (Pol I) inhibition in vitro and in vivo. Moreover Cdc14-dependent inhibition involves nucleolar exclusion of Pol I subunits. We demonstrate that transcription inhibition is necessary for complete chromosome disjunction, because ribosomal RNA (rRNA) transcripts block condensin binding to rDNA, and show that bypassing the role of Cdc14 in nucleolar segregation requires in vivo degradation of nascent transcripts. Our results show that transcription interferes with chromosome condensation, not the reverse. We conclude that budding yeast, like most eukaryotes, inhibit Pol I transcription before segregation as a prerequisite for chromosome condensation and faithful genome separation.

RNA polymerase I structure and transcription regulation

“…42), which may be dephosphorylated during the cell cycle by the Cdc14 phosphatase that inhibits Pol I (ref. 43). …”

Rio1 promotes rDNA stability and downregulates RNA polymerase I to ensure rDNA segregation

“…PolI downregulation in anaphase is mediated by the Cdc14 phosphatase acting on PolI subunit Rpa43 (ref. 4), resulting in PolI dissociating from the 35S rDNA. The removal of PolI and the local resolution of its transcripts allow the condensin complex to bind.…”

“…Processing of the 35S pre-rRNA generates 5.8S, 18S and 25S rRNA that, together with the 5S rRNA, become the catalytic backbones of each ribosome 5,6 . Only in anaphase does yeast repress rDNA transcription 4 , which allows the sister rDNA loci to condensate and segregate. PolI downregulation in anaphase is mediated by the Cdc14 phosphatase acting on PolI subunit Rpa43 (ref.…”

“…A t anaphase onset, the replicated chromosomes separate and then segregate along the mitotic spindle into the daughter cells. In the budding yeast Saccharomyces cerevisiae, the locus containing the genes that encode the ribosomal RNAs (rDNA) segregates after the rest of the genome, in late anaphase [1][2][3][4] . The rDNA locus exists as a tandem-repeat array comprising B150 rDNA units containing the 35S and 5S genes, which are transcribed by RNA polymerase I (PolI) and PolIII, respectively.…”

Does transcription play a role in creating a condensin binding site?

“…3 Similarly, RNAP I must be inhibited before condensin can associate with the rDNA. 4 Overall, these data argue that active transcription represents an obstacle for the binding of condensin.…”