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J Biol Chem. 2001 Mar 16;276(11):8616-22. Epub 2000 Dec 15.

Nam1p, a protein involved in RNA processing and translation, is coupled to transcription through an interaction with yeast mitochondrial RNA polymerase.

Author information

1
Department of Biochemistry, Emory University School of Medicine, Rollins Research Center, Atlanta, Georgia 30322, USA.

Abstract

Alignment of three fungal mtRNA polymerases revealed conserved amino acid sequences in an amino-terminal region of the Saccharomyces cerevisiae enzyme implicated previously as harboring an important functional domain. Phenotypic analysis of deletion and point mutations, in conjunction with a yeast two-hybrid assay, revealed that Nam1p, a protein involved in RNA processing and translation in mitochondria, binds specifically to this domain. The significance of this interaction in vivo was demonstrated by the fact that the temperature-sensitive phenotype of a deletion mutation (rpo41Delta2), which impinges on this amino-terminal domain, is suppressed by overproducing Nam1p. In addition, mutations in the amino-terminal domain result specifically in decreased steady-state levels of mature mitochondrial CYTB and COXI transcripts, which is a primary defect observed in NAM1 null mutant yeast strains. Finally, one point mutation (R129D) did not abolish Nam1p binding, yet displayed an obvious COX1/CYTB transcript defect. This mutation exhibited the most severe mitochondrial phenotype, suggesting that mutations in the amino-terminal domain can perturb other critical interactions, in addition to Nam1p binding, that contribute to the observed phenotypes. These results implicate the amino-terminal domain of mtRNA polymerases in coupling additional factors and activities involved in mitochondrial gene expression directly to the transcription machinery.

PMID:
11118450
PMCID:
PMC2606050
DOI:
10.1074/jbc.M009901200
[Indexed for MEDLINE]
Free PMC Article

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