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Scc-3

Scc-3. Naznin Daginawala. Clones Analyzed. Six clones were sequenced 2: 28S rRNA 2: 18S rRNA F52E1.13 Hypothetical protein containing a LsyM domain Scc-3. Blast Search. Blast search revealed the cDNA had been sequenced by a member of last year’s class. Perfect match

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Scc-3

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  1. Scc-3 Naznin Daginawala

  2. Clones Analyzed • Six clones were sequenced • 2: 28S rRNA • 2: 18S rRNA • F52E1.13 • Hypothetical protein containing a LsyM domain • Scc-3

  3. Blast Search • Blast search revealed the cDNA had been sequenced by a member of last year’s class • Perfect match • Overlaps with last 446 bp of published sequence

  4. Gene Structure • Insert spans 2 introns • Overlaps exons 3, 4, and 5 of C. elegans homolog • ORF was found in the -2 reading frame

  5. Orthologs of Scc-3 • The Scc3 family includes known orthologs from a variety of fungi, plants, and animals • Scc-3 is highly conserved from yeast to humans • Humans and mice: 56% similarity to STAG3 • Yeast: 48% similarity to IRR1 (SCC3)

  6. Protein Structure and Conserved Domains • Encodes a protein with 1096 amino acids • Conserved domains • stromal antigen domain (SA/STAG) • Armadillo-like helical • consists of a multi-helical fold comprised of alpha helices • well suited to binding large substrates such as proteins and nucleic acids

  7. Biological Function • Member of a “cohesin” complex that serves to ensure sister chromatid cohesion during mitosis and meiosis • Complex is present from S phase until the onset of anaphase • Sister chromatid cohesion and attachment of kinetochores to opposite poles of the mitotic spindle must be carefully coordinated for proper segregation

  8. Cohesin Complex • Four core subunits • Smc1 and Smc3 form a heterodimer and belong to the structural maintenance of chromosomes family • Scc1 or Rec8 in meiosis • Scc3

  9. RNAi Phenotype • RNAi feeding was performed • 1.2% of the F1 progeny was viable compared to the wt control group 94% • Surviving progeny showed abnormal meiosis/mitosis A) Nuclei of variable size B) Anaphase bridges Pasierbek et al, 2003

  10. Role in Double Stranded Break Repair • RAD51 is a protein that associates with double stranded breaks • In Scc-3 RNAi phenotype, RAD51 is present at irregular time points indicating defective dsb repair Pasierbek et al, 2003

  11. Human STAG Family • Scc-3 is an ortholog of the human STAG1, STAG2 and STAG3 family of genes • Clinical relevance in humans • An understanding of cohesion/separation is essential to study the causes of aneuploidies and infertility • Cancer • Expression of STAG1 mediates p53 dependant apoptosis

  12. Future Directions • The mechanism by which the cohesin ring structure is assembled is not well understood • Role of Scc-3 is unknown except that it plays some essential role in sister chromatid cohesion • Use of STAG1 in gene therapy

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