Interaction between mitochondrial genes in yeast: evidence for novel box effect(s)

Area of Science:

• Mitochondrial gene expression
• RNA processing
• Molecular genetics

Background:

• The apocytochrome b gene contains introns crucial for regulating the expression of other genes, including cytochrome c oxidase subunit I (coxI).
• Mutations within these introns can disrupt normal RNA processing pathways.

Purpose of the Study:

• To investigate the effects of mutations in the apocytochrome b gene on the processing of coxI transcripts.
• To elucidate the role of apocytochrome b introns in coxI RNA maturation and gene expression.

Main Methods:

• Analysis of RNA transcripts from various mutants in the apocytochrome b gene using hybridization techniques.
• Characterization of aberrant OXI3 transcripts (pre-mRNAs for coxI) in mutant strains.
• Complementation studies to assess the functional interaction between different mutation sites.

Main Results:

• Mutations in the fourth intron (bI4) of the apocytochrome b gene primarily cause failure to remove intron aI4 from coxI precursor transcripts.
• Mutations in other introns (bI2, bI3) lead to complex processing defects, generating novel OXI3 transcripts of varying sizes.
• Specific mutations (box9, box7) result in the absence or reduction of 18S mRNA for cytochrome c oxidase subunit I, indicating severe processing deficiencies.

Conclusions:

• Aberrant RNA processing events, such as cut-no-splice, occur at different intron-exon borders of OXI3 pre-RNAs depending on the mutation site within the apocytochrome b gene.
• The 'box effect,' an interaction between split genes, is not solely mediated by the box7 element, suggesting broader regulatory roles for apocytochrome b introns.
• Mutated intronic reading frames within the apocytochrome b gene may produce aberrant products that interfere with coxI transcript processing.