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Gene Review

FOB1  -  Fob1p

Saccharomyces cerevisiae S288c

Synonyms: DNA replication fork-blocking protein FOB1, HRM1, YD9727.06, YDR110W
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Disease relevance of FOB1


High impact information on FOB1

  • It is known that mutations in gene SIR2 increase and those in FOB1 decrease recombination within rDNA repeats as assayed by marker loss or extrachromosomal rDNA circle formation [2].
  • Because rrm3-induced increases in recombination and cell cycle length were only partially suppressed in rrm3 fob1 cells, which still required checkpoint and fork restart activities for viability, non-RFB rrm3-induced defects contribute to rDNA fragility and genome instability [3].
  • We find that Net1 and Sir2 are physically associated with Fob1 and subunits of RNA polymerase I. Together with the localization data, these results suggest the existence of two distinct modes for the recruitment of the RENT complex to rDNA and reveal a role for Fob1 in rDNA silencing and in the recruitment of the RENT complex [4].
  • In cells lacking Fob1, silencing and the association of RENT subunits are abolished specifically at NTS1, while silencing and association at the Pol I promoter region are unaffected or increased [4].
  • FOB1 was shown previously to be required for replication fork blocking (RFB) activity at RFB site in rDNA and for recombination hot-spot (HOT1) activity [5].

Biological context of FOB1

  • FOB1 showed a gene dosage effect on not only the amounts of both recombinants, but also on the copy number of the repeat [6].
  • In addition, FOB1 may also play a role in the copy number regulation of rDNA tandem repeats [6].
  • Orientation of the RFB sequence in its inactive course or its abolition by FOB1 deletion avoided plasmid integration in sir2 mutant cells, indicating that stalling of the forks in the plasmid context was required for recombination to take place [7].
  • FOB1 is required for recombination hot spot (HOT1) activity, which also requires the enhancer region, and for recombination within rDNA repeats [8].
  • These results indicate that FOB1 plays a novel role in preventing repeat contraction by regulating condensin association and suggest a link between replication termination and chromosome condensation and segregation [9].

Anatomical context of FOB1

  • Deletion of FOB1 and overexpression of SIR2 have been previously found to increase life span by reducing the levels of toxic rDNA circles in aged mother cells [10].
  • The rapid-aging phenotype of sip2 Delta cells is fully rescued by blocking recombination at rDNA loci with a fob1 Delta allele; rescue is not accompanied by amelioration of an age-associated shift toward gluconeogenesis and glucose storage [11].

Associations of FOB1 with chemical compounds

  • However, even in cells lacking both Sir2 and the replication fork block protein Fob1, nicotinamide partially prevents life span extension by CR [12].

Physical interactions of FOB1


Co-localisations of FOB1

  • Hmo1 co-localizes with Fob1, a known rDNA-binding protein, defining a narrow territory adjacent to the nucleoplasm that could delineate the rDNA nucleolar domain [14].

Regulatory relationships of FOB1

  • The short life span of a sir2 mutant also reveals a direct failure to repress recombination generated by the Fob1p-mediated replication block in the rDNA [15].

Other interactions of FOB1

  • FOB1, which is known to be required for ERC formation, and RTG2 were found to be in converging pathways for ERC production [16].
  • However, unlike the RAD52 gene, the FOB1 gene was not involved in homologous recombination in a non-rDNA locus [6].
  • Either deletion of FOB1, which suppresses fork blocking and certain types of rDNA recombination, or an increase in SIR2 gene dosage, which suppresses rDNA recombination, reduces the number of forks persisting at the RFB [17].
  • Conversely, high levels of FOB1 delay the release of Cdc14 from the nucleolus [13].
  • FOB1 affects DNA topoisomerase I in vivo cleavages in the enhancer region of the Saccharomyces cerevisiae ribosomal DNA locus [18].

Analytical, diagnostic and therapeutic context of FOB1


  1. A model of the replication fork blocking protein Fob1p based on the catalytic core domain of retroviral integrases. Dlakić, M. Protein Sci. (2002) [Pubmed]
  2. SIR2 regulates recombination between different rDNA repeats, but not recombination within individual rRNA genes in yeast. Kobayashi, T., Horiuchi, T., Tongaonkar, P., Vu, L., Nomura, M. Cell (2004) [Pubmed]
  3. Local chromatin structure at the ribosomal DNA causes replication fork pausing and genome instability in the absence of the S. cerevisiae DNA helicase Rrm3p. Torres, J.Z., Bessler, J.B., Zakian, V.A. Genes Dev. (2004) [Pubmed]
  4. Association of the RENT complex with nontranscribed and coding regions of rDNA and a regional requirement for the replication fork block protein Fob1 in rDNA silencing. Huang, J., Moazed, D. Genes Dev. (2003) [Pubmed]
  5. Expansion and contraction of ribosomal DNA repeats in Saccharomyces cerevisiae: requirement of replication fork blocking (Fob1) protein and the role of RNA polymerase I. Kobayashi, T., Heck, D.J., Nomura, M., Horiuchi, T. Genes Dev. (1998) [Pubmed]
  6. Replication fork block protein, Fob1, acts as an rDNA region specific recombinator in S. cerevisiae. Johzuka, K., Horiuchi, T. Genes Cells (2002) [Pubmed]
  7. Sir2p suppresses recombination of replication forks stalled at the replication fork barrier of ribosomal DNA in Saccharomyces cerevisiae. Benguría, A., Hernández, P., Krimer, D.B., Schvartzman, J.B. Nucleic Acids Res. (2003) [Pubmed]
  8. Yeast RNA polymerase I enhancer is dispensable for transcription of the chromosomal rRNA gene and cell growth, and its apparent transcription enhancement from ectopic promoters requires Fob1 protein. Wai, H., Johzuka, K., Vu, L., Eliason, K., Kobayashi, T., Horiuchi, T., Nomura, M. Mol. Cell. Biol. (2001) [Pubmed]
  9. Condensin loaded onto the replication fork barrier site in the rRNA gene repeats during S phase in a FOB1-dependent fashion to prevent contraction of a long repetitive array in Saccharomyces cerevisiae. Johzuka, K., Terasawa, M., Ogawa, H., Ogawa, T., Horiuchi, T. Mol. Cell. Biol. (2006) [Pubmed]
  10. Sir2-independent life span extension by calorie restriction in yeast. Kaeberlein, M., Kirkland, K.T., Fields, S., Kennedy, B.K. PLoS Biol. (2004) [Pubmed]
  11. Sip2, an N-myristoylated beta subunit of Snf1 kinase, regulates aging in Saccharomyces cerevisiae by affecting cellular histone kinase activity, recombination at rDNA loci, and silencing. Lin, S.S., Manchester, J.K., Gordon, J.I. J. Biol. Chem. (2003) [Pubmed]
  12. Increased life span due to calorie restriction in respiratory-deficient yeast. Kaeberlein, M., Hu, D., Kerr, E.O., Tsuchiya, M., Westman, E.A., Dang, N., Fields, S., Kennedy, B.K. PLoS Genet. (2005) [Pubmed]
  13. The replication fork block protein Fob1 functions as a negative regulator of the FEAR network. Stegmeier, F., Huang, J., Rahal, R., Zmolik, J., Moazed, D., Amon, A. Curr. Biol. (2004) [Pubmed]
  14. Hmo1, an HMG-box protein, belongs to the yeast ribosomal DNA transcription system. Gadal, O., Labarre, S., Boschiero, C., Thuriaux, P. EMBO J. (2002) [Pubmed]
  15. The SIR2/3/4 complex and SIR2 alone promote longevity in Saccharomyces cerevisiae by two different mechanisms. Kaeberlein, M., McVey, M., Guarente, L. Genes Dev. (1999) [Pubmed]
  16. Rtg2 protein links metabolism and genome stability in yeast longevity. Borghouts, C., Benguria, A., Wawryn, J., Jazwinski, S.M. Genetics (2004) [Pubmed]
  17. Evidence that yeast SGS1, DNA2, SRS2, and FOB1 interact to maintain rDNA stability. Weitao, T., Budd, M., Campbell, J.L. Mutat. Res. (2003) [Pubmed]
  18. FOB1 affects DNA topoisomerase I in vivo cleavages in the enhancer region of the Saccharomyces cerevisiae ribosomal DNA locus. Di Felice, F., Cioci, F., Camilloni, G. Nucleic Acids Res. (2005) [Pubmed]
  19. Transcription-dependent recombination and the role of fork collision in yeast rDNA. Takeuchi, Y., Horiuchi, T., Kobayashi, T. Genes Dev. (2003) [Pubmed]
  20. The replication fork barrier site forms a unique structure with Fob1p and inhibits the replication fork. Kobayashi, T. Mol. Cell. Biol. (2003) [Pubmed]
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