Disease relevance of BI4

• The bI4 RNA mitochondrial maturase of Saccharomyces cerevisiae can stimulate intra-chromosomal recombination in Escherichia coli [1].

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].

References