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Gene Review

BI3  -  cytochrome b mRNA maturase bI3

Saccharomyces cerevisiae S288c

Synonyms: Cytochrome b mRNA maturase bI3, Q0115, bI3
 
 
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High impact information on BI3

  • The bI3 maturase binds as a monomer, whereas Mrs1 is a dimer in solution that assembles as two dimers, cooperatively, on the RNA [1].
  • (1) In the absence of Mg(2+), two Mrs1 dimers bind independently to the bI3 RNA [2].
  • Cytoduction experiments show that a mitochondrial genome deleted for the three introns bI3, aI5 and aI6 is able to suppress the pet157-1 mutation: the strain recovers respiratory competency indicating that the product of the PET157 gene is only required for mitochondrial pre-mRNA splicing [3].
  • Each of the inserts, when present in high copy number, has a similar suppressor activity: high in the presence of mutation M1301 in bI1, a group II intron, and low but significant with the presence of few mutants in bI2 and bI3 of the COB gene, both of which are group I introns [4].
  • When combined with mitochondrial genomes lacking introns bI1, bI2 and bI3, or lacking intron bI3 alone the mutant is respiratory competent [5].
 

Biological context of BI3

  • Hybridization experiments showed, that it is (i) a single copy gene, (ii) also present in strain D273-10B, containing the "short form" mitochondrial genome (lacking the COB introns bI1-bI3), and (iii) located on chromosome IX [5].
  • This, together with the defects observed in bI2 and bI3 mutants, implies that the box effect (i.e., the interaction between these two split genes) is not mediated by the box7 element alone [6].
  • (4) Maturase and Mrs1 proteins each bind the bI3 RNA tightly, but with only modest coupling (approximately 1 kcal/mol), suggesting that the proteins interact at independent RNA binding sites [2].
 

Anatomical context of BI3

  • (5) At effective concentrations plausibly present in yeast mitochondria, a predominant assembly pathway emerges involving rapid, tight binding by the bI3 maturase, followed by slower, cooperative assembly of two Mrs1 dimers [2].
 

Associations of BI3 with chemical compounds

  • In this report, crystallographic analysis shows that the global architecture of the bI3 maturase is unchanged from its DNA-binding homologs; in contrast, the endonuclease active site, dispensable for splicing facilitation, is efficiently compromised by a lysine residue replacing essential catalytic groups [7].
 

Other interactions of BI3

  • Cloning of a nuclear gene MRS1 involved in the excision of a single group I intron (bI3) from the mitochondrial COB transcript in S. cerevisiae [5].
  • The involvement of this nuclear gene in the excision of a single group I mitochondrial intron (bI3) of the COB transcript is discussed [5].
 

Analytical, diagnostic and therapeutic context of BI3

  • We have shown by restriction analysis and allelism tests that the pet157-1 mutation is allelic to the nuclear mrs1 mutation, previously described as specifically blocking the excision of bI3 [3].

References

  1. Recruitment of intron-encoded and co-opted proteins in splicing of the bI3 group I intron RNA. Bassi, G.S., de Oliveira, D.M., White, M.F., Weeks, K.M. Proc. Natl. Acad. Sci. U.S.A. (2002) [Pubmed]
  2. Kinetic and thermodynamic framework for assembly of the six-component bI3 group I intron ribonucleoprotein catalyst. Bassi, G.S., Weeks, K.M. Biochemistry (2003) [Pubmed]
  3. Two group I mitochondrial introns in the cob-box and coxI genes require the same MRS1/PET157 nuclear gene product for splicing. Bousquet, I., Dujardin, G., Poyton, R.O., Slonimski, P.P. Curr. Genet. (1990) [Pubmed]
  4. Three nuclear genes suppress a yeast mitochondrial splice defect when present in high copy number. Koll, H., Schmidt, C., Wiesenberger, G., Schmelzer, C. Curr. Genet. (1987) [Pubmed]
  5. Cloning of a nuclear gene MRS1 involved in the excision of a single group I intron (bI3) from the mitochondrial COB transcript in S. cerevisiae. Kreike, J., Schulze, M., Pillar, T., Körte, A., Rödel, G. Curr. Genet. (1986) [Pubmed]
  6. Interaction between mitochondrial genes in yeast: evidence for novel box effect(s). Hensgens, L.A., Van der Horst, G., Grivell, L.A. Plasmid (1984) [Pubmed]
  7. Evolution from DNA to RNA recognition by the bI3 LAGLIDADG maturase. Longo, A., Leonard, C.W., Bassi, G.S., Berndt, D., Krahn, J.M., Hall, T.M., Weeks, K.M. Nat. Struct. Mol. Biol. (2005) [Pubmed]
 
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