Autophagy deficiency activates rDNA transcription

Nucleolin is a ubiquitous multifunctional protein involved in preribosome assembly and associated with both nucleolar chromatin in interphase and nucleolar organizer regions on metaphasic chromosomes in mitosis. Extensive nucleolin phosphorylation by a casein kinase (CKII) occurs on serine in growing cells. Here we report that while CKII phosphorylation is achieved in interphase, threonine phosphorylation occurs during mitosis. We provide evidence that this type of in vivo phosphorylation involves a mammalian homolog of the cell cycle control Cdc2 kinase. In vitro M-phase H1 kinase from starfish oocytes phosphorylated threonines in a TPXK motif present nine times in the amino-terminal part of the protein. The same sites which matched the p34cdc2 consensus phosphorylation sequence were used in vivo during mitosis. We propose that successive Cdc2 and CKII phosphorylation could modulate nucleolin function in controlling cell cycle-dependent nucleolar function and organization. Our results, along with previous studies, suggest that while serine phosphorylation is related to nucleolin function in the control of rDNA transcription, threonine phosphorylation is linked to mitotic reorganization of nucleolar chromatin.

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When rDNA transcription is arrested during mitosis, UBF is still associated with non-condensed rDNA

Journal of Cell Science ◽

10.1242/jcs.110.19.2429 ◽

1997 ◽

Vol 110 (19) ◽

pp. 2429-2440 ◽

Cited By ~ 4

Author(s):

J. Gebrane-Younes ◽

N. Fomproix ◽

D. Hernandez-Verdun

Keyword(s):

Secondary Constriction ◽

Three Dimensional ◽

Ribosomal Gene ◽

Rdna Transcription ◽

Transcription Machinery ◽

Late Anaphase ◽

Early Anaphase ◽

Dimensional Distribution ◽

Open Question ◽

Kinetics Of

The mechanisms that control inactivation of ribosomal gene (rDNA) transcription during mitosis is still an open question. To investigate this fundamental question, the precise timing of mitotic arrest was established. In PtK1 cells, rDNA transcription was still active in prophase, stopped in prometaphase until early anaphase, and activated in late anaphase. Because rDNA transcription can still occur in prophase and late anaphase chromosomes, the kinetics of rDNA condensation during mitosis was questioned. The conformation of the rDNA was analyzed by electron microscopy from the G2/M transition to late anaphase in the secondary constriction, the chromosome regions where the rDNAs are clustered. Whether at transcribing or non-transcribing stages, non-condensed rDNA was observed in addition to axial condensed rDNA. Thus, the persistence of this non-condensed rDNA during inactive transcription argues in favor of the fact that mitotic inactivation is not the consequence of rDNA condensation. Analysis of the three-dimensional distribution of the rDNA transcription factor, UBF, revealed that it was similar at each stage of mitosis in the secondary constriction. In addition, the colocalization of UBF with non-condensed rDNA was demonstrated. This is the first visual evidence of the association of UBF with non-condensed rDNA. As we previously reported that the rDNA transcription machinery remained assembled during mitosis, the colocalization of rDNA fibers with UBF argues in favor of the association of the transcription machinery with certain rDNA copies even in the absence of transcription. If this hypothesis is correct, it can be assumed that condensation of rDNA as well as dissociation of the transcription machinery from rDNA cannot explain the arrest of rDNA transcription during mitosis. It is proposed that modifications of the transcription machinery occurring in prometaphase could explain the arrest of transcription, while reverse modifications in late anaphase could explain activation.

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The mitotically phosphorylated form of the transcription termination factor TTF-1 is associated with the repressed rDNA transcription machinery

Journal of Cell Science ◽

10.1242/jcs.112.19.3259 ◽

1999 ◽

Vol 112 (19) ◽

pp. 3259-3268 ◽

Cited By ~ 2

Author(s):

V. Sirri ◽

P. Roussel ◽

D. Hernandez-Verdun

Keyword(s):

Transcription Termination ◽

Nucleolar Organizer ◽

Ribosomal Gene ◽

Nucleolar Organizer Regions ◽

Rdna Transcription ◽

Mitotic Chromosomes ◽

Termination Factor ◽

Transcription Machinery ◽

Phosphorylated Form ◽

Transcription Termination Factor

The transcription termination factor TTF-1 exerts two functions in ribosomal gene (rDNA) transcription: facilitating initiation and mediating termination of transcription. Using HeLa cells, we show that TTF-1 protein is colocalized with the active transcription machinery in the nucleolus and also with the inactive machinery present in certain mitotic nucleolar organizer regions (NORs) when rDNA transcription is repressed. We also show that TTF-1 is specifically phosphorylated during mitosis in a manner dependent on the cdc2-cyclin B kinase pathway and on an okadaic acid-sensitive phosphatase. Interestingly, the mitotically phosphorylated form of TTF-1 appearing at the G(2)/M transition phase was more easily solubilized than was the interphase form. This indicates that the chromatin-binding affinity of TTF-1 appears to be different in mitotic chromosomes compared to the interphase nucleolus. Correlated with this, the other DNA-binding factor, UBF, which interferes with chromatin conformation in the rDNA promoter, was more strongly bound to rDNA during mitosis than at interphase. The reorganization of the mitotic rDNA promoter might be induced by phosphorylation of certain components of the rDNA transcription machinery and participate in silencing of rDNA during mitosis.

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Preferential inhibition of rDNA transcription by 5-bromodeoxyuridine

Journal of Cell Science ◽

10.1242/jcs.25.1.95 ◽

1977 ◽

Vol 25 (1) ◽

pp. 95-102

Author(s):

A.E. Lykkesfeldt ◽

H.A. Andersen

Keyword(s):

Growth Medium ◽

Ribosomal Rna ◽

Rna Synthesis ◽

Tetrahymena Pyriformis ◽

Degree Of Substitution ◽

Rdna Transcription ◽

Total Rna

On a chemically defined growth medium the degree of substitution of thymidine with 5-bromodeoxyuridine (BUdR) in DNA of Tetrahymena pyriformis was controlled by the concentration of tetrahydrofiolic acid, BUdR and thymidine in the medium. A correlation between the degree of BUdR substitution in DNA and the reduction in rate of total RNA synthesis has been established. It was found that the reduction of total RNA synthesis results from inhibition of transcription of all RNA species which have been measured. However, independent of the degree of BUdR substitution in DNA, a preferential inhibition of the synthesis of 25s and 17s ribosomal RNA was found. It is concluded that the various genes may respond differently to BUdR substitution with respect to transcription.

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Species-specific rDNA transcription is due to promoter-specific binding factors.

Molecular and Cellular Biology ◽

10.1128/mcb.4.2.221 ◽

1984 ◽

Vol 4 (2) ◽

pp. 221-227 ◽

Cited By ~ 42

Author(s):

R Miesfeld ◽

N Arnheim

Keyword(s):

Rna Polymerase ◽

Transcriptional Control ◽

Specific Binding ◽

Rna Polymerase I ◽

Rdna Transcription ◽

Nucleolar Dominance ◽

Cell Extracts ◽

Species Specific ◽

Polymerase I

RNA polymerase I transcription factors were purified from HeLa and mouse L cell extracts by phosphocellulose chromatography. Three fractions from each species were found to be required for transcription. One of these fractions, virtually devoid of RNA polymerase I activity, was found to form a stable preinitiation complex with small DNA fragments containing promoter sequences from the homologous but not the heterologous species. These species-specific DNA-binding factors can explain nucleolar dominance in vivo in mouse-human hybrid somatic cells and species specificity in cell-free, RNA polymerase I-dependent transcription systems. The evolution of species-specific transcriptional control signals may be the natural outcome of a special relationship that exists between the RNA polymerase I transcription machinery and the multigene family coding for rRNA.

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