Chromatin association and regulation of rDNA transcription by the Ras-family protein RasL11a.
RasL11a and RasL11b are Ras super-family proteins of unknown function. Here, we show that RasL11a is a chromatin-associated modulator of pre-ribosomal RNA (pre-rRNA) synthesis. RasL11a was found in the nucleolus of interphase mouse fibroblasts, where it co-localized with the RNA polymerase I-specific transcription factor UBF. Similar to UBF, RasL11a also marked the active subset of rDNA repeats (also called nucleolar organizers, or NORs) on mitotic chromosomes. In cells, RasL11a existed in stable complexes with UBF and, as shown by chromatin immunoprecipitation, distributed along the rDNA transcription unit. Upon treatment of cells with actinomycin D, RasL11a and UBF persisted on the transcription unit beyond the release of RNA polymerase I, and remained co-localized in peri-nucleolar cap structures. Ectopic expression of RasL11a enhanced pre-rRNA levels in cells, whereas RasL11a knockdown had the opposite effect. In transient transfection experiments, RasL11a enhanced the transcriptional activity of an RNA polymerase I-specific reporter controlled by the rDNA enhancer/promoter region. We speculate that RasL11a acts in concert with UBF to facilitate initiation and/or elongation by RNA polymerase I in response to specific upstream stimuli.
Pistoni
Mariaelena
M
Department of Experimental Oncology, European Institute of Oncology, IFOM-IEO Campus, Milan, Italy.
Verrecchia
Alessandro
A
Doni
Mirko
M
Guccione
Ernesto
E
Amati
Bruno
B
D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000737:chemistry; D002843:Chromatin / Q000378:metabolism*; D004275:DNA, Ribosomal / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D041681:NIH 3T3 Cells; D035463:Pol1 Transcription Initiation Complex Proteins / Q000032:analysis / Q000378:metabolism; D012318:RNA Polymerase I / Q000378:metabolism; D014158:Transcription, Genetic
D002843:Chromatin; D004275:DNA, Ribosomal; D035463:Pol1 Transcription Initiation Complex Proteins; C063844:transcription factor UBF; D012318:RNA Polymerase I; C484949:RASL11A protein, human; C549012:RASL11A protein, mouse; D020559:Monomeric GTP-Binding Proteins