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Gene Review

BI4  -  intron-encoded RNA maturase bI4

Saccharomyces cerevisiae S288c

Synonyms: Intron-encoded RNA maturase bI4, Q0120, RNA maturase SCbI4, SCBI4, bI4
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Disease relevance of BI4


High impact information on BI4

  • bI4 maturase, encoded by the fourth intron of the yeast mitochondrial cytochrome b gene, controls the splicing of both the fourth intron of the cytochrome b gene and the fourth intron of the gene encoding subunit I of cytochrome oxidase [2].
  • The resulting protein is imported into mitochondria, which was revealed by its ability to restore to respiratory competence a yeast mutant defective in the bI4 maturase [2].
  • By fusing the encoding presequence of subunit 9 of the Neurospora ATPase to a restriction fragment containing the bI4 maturase coding sequence, we have constructed a hybrid gene that can be translated on yeast cytosolic ribosomes [2].
  • Yeast mitochondrial leucyl-tRNA synthetase (LeuRS) binds to the bI4 intron and collaborates with the bI4 maturase to aid excision of the group I intron [3].
  • Interestingly, all the genes lead to the synthesis of cytochrome b, while only the genes having the intron bI4 allow the expression of oxi3 [4].

Biological context of BI4

  • We conclude that the mLRS is a splicing factor essential for the excision of the group I introns bI4 and aI4 and probably important for the excision of other group I introns [5].
  • Dominant mutations in the yeast nuclear gene NAM2 cure the RNA splicing deficiency resulting from the inactivation of the bI4 maturase encoded by the fourth intron of the mitochondrial cytochrome b gene [6].
  • The products of those gene fusions suppress the bI4 maturase deficiency still present in those heteroplasmic cells [7].
  • These data combined with previous genetic results are consistent with a novel model for a ternary splicing complex (two protein: one RNA) in which both protein splicing partners bind directly to the bI4 intron and facilitate its self-splicing activity [8].
  • In the presence of either the bI4 maturase or the Leu-tRNA synthetase, bI4 intron transcribed recombinantly with flanking exons in the yeast nucleus exhibited splicing activity [8].

Associations of BI4 with chemical compounds

  • They were found to be heteroplasmic cells owing their regained ability to respire (and grow on glycerol medium) to the presence of a rearranged (rho-) mtDNA that contains an in-frame fusion of the reading frames of the group I introns bI4 and intron 4 alpha of the coxl gene encoding subunit I of cytochrome c oxidase (aI4 alpha) [7].

Regulatory relationships of BI4

  • In each case, interactions with only the LeuRS protein fragment specifically stimulated bI4 intron splicing activity [3].

Other interactions of BI4

  • The fact that these loci complement each other (B. Weiss-Brummer, G. Rödel, R.J. Schweyen, and F. Kaudewitz (1982) Cell 29, 527-536), therefore, suggests that mutations within the different functional domains of bI4 lead to different defects in the processing of OXI3 transcripts [9].
  • These data indicate an obligatory connection between mitoribosome function and splicing of introns bI2, bI4 and aI1 in yeast mitochondria [10].


  1. The bI4 RNA mitochondrial maturase of Saccharomyces cerevisiae can stimulate intra-chromosomal recombination in Escherichia coli. Goguel, V., Bailone, A., Devoret, R., Jacq, C. Mol. Gen. Genet. (1989) [Pubmed]
  2. A mitochondrial RNA maturase gene transferred to the yeast nucleus can control mitochondrial mRNA splicing. Banroques, J., Delahodde, A., Jacq, C. Cell (1986) [Pubmed]
  3. An inserted region of leucyl-tRNA synthetase plays a critical role in group I intron splicing. Rho, S.B., Lincecum, T.L., Martinis, S.A. EMBO J. (2002) [Pubmed]
  4. Construction of novel cytochrome b genes in yeast mitochondria by subtraction or addition of introns. Labouesse, M., Slonimski, P.P. EMBO J. (1983) [Pubmed]
  5. The yeast mitochondrial leucyl-tRNA synthetase is a splicing factor for the excision of several group I introns. Labouesse, M. Mol. Gen. Genet. (1990) [Pubmed]
  6. The yeast nuclear gene NAM2 is essential for mitochondrial DNA integrity and can cure a mitochondrial RNA-maturase deficiency. Labouesse, M., Dujardin, G., Slonimski, P.P. Cell (1985) [Pubmed]
  7. Novel hybrid maturases in unstable pseudorevertants of maturaseless mutants of yeast mitochondrial DNA. Anziano, P.Q., Moran, J.V., Gerber, D., Perlman, P.S. Nucleic Acids Res. (1990) [Pubmed]
  8. The bI4 group I intron binds directly to both its protein splicing partners, a tRNA synthetase and maturase, to facilitate RNA splicing activity. Rho, S.B., Martinis, S.A. RNA (2000) [Pubmed]
  9. 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]
  10. Nuclear omnipotent suppressors of premature termination codons in mitochondrial genes affect the 37S mitoribosomal subunit. Boguta, M., Mieszczak, M., Zagórski, W. Curr. Genet. (1988) [Pubmed]
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