Ms. Rodeheffer et al., Nam1p, a protein involved in RNA processing and translation, is coupled totranscription through an interaction with yeast mitochondrial RNA polymerase, J BIOL CHEM, 276(11), 2001, pp. 8616-8622
Alignment of three fungal mtRNA polymerases revealed conserved amino acid s
equences in an aminoterminal region of the Saccharomyces cerevisiae enzyme
implicated previously as harboring an important functional domain. Phenotyp
ic analysis of deletion and point mutations, in conjunction with a yeast tw
o-hybrid assay, revealed that Nam1p, a protein involved in RNA processing a
nd translation in mitochondria, binds specifically to this domain, The sign
ificance of this interaction in vivo was demonstrated by the fact that the
temperature-sensitive phenotype of a deletion mutation (rpo41 Delta2), whic
h impinges on this amino-terminal domain, is suppressed by overproducing Na
m1p. In addition, mutations in the amino-terminal domain result specificall
y in decreased steady-state levels of mature mitochondrial CYTB and COXI tr
anscripts, which is a primary defect observed in NAM1 null mutant yeast str
ains. Finally, one point mutation (R129D) did not abolish Nam1p binding, ye
t 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 addit
ional factors and activities involved in mitochondrial gene expression dire
ctly to the transcription machinery.