Abstract: Mitochondrial gene expression

[Robert Brambl]

Expression of Mitochondrial Genes in the Germinating Conidia of Neurospora  
crassa

Peter Bitner-Eddy, Antonio F. Monroy and Robert Brambl
J. Mol. Biol. (1994) 235: 881-897

Summary:
The germinating asexual spores (conidia) of Neurospora crassa were  
employed to study steps in the accumulation of transcripts of groups of  
mitochondrial genes, including those for peptide subunits of cytochrome c  
oxidase (CO), ATPase (ATP), and apocytochrome b (COB). Physically  
clustered groups of genes were expressed as cohorts: transcripts of the  
ATP8-ATP6-mtATP9-CO2 genes were almost undetectable in the dormant spores,  
and they accumulated rapidly as a group immediately after spore  
activation. Transcripts of COB and the adjacent CO1 were abundant in the  
dormant spores, and the dormant and germinating spores contained size  
forms of the COB transcripts that were not evident in vegetative cells.  
Polyribosomes were prepared from mitochondrial lysates, and the  
polyribosomal RNA was probed to identify the mRNAs of specific genes; in  
several instances polycistronic mRNAs were present in the polyribosomes as  
were the smaller end-products of the inferred transcript processing  
pathways. The expression of the physically dispersed genes for subunit  
peptides of cytochrome c oxidase appears to be regulated at the level of  
translation; these transcripts are accumulated in the total mitochondrial  
RNA with sharply different kinetics, but they appeared in the  
polyribosomes uniformly, their appearance correlating with the uniform  
synthesis of the subunit peptides. Transcripts for a previously reported  
non-functional mitochondrial gene, homologous to the functional nuclear  
gene for ATPase subunit 9, were found in the germinating spores, but were  
not detected in vegetative cells. These mtATP9 transcripts were also  
present in the polyribosomes and were apparently translated into a protein  
in vivo whose synthesis was insensitive to cycloheximide and detectable  
with an anti-ATP9 subunit antibody. Transcripts for two nuclear genes for  
mitochondrially localized proteins, ATP9 and CO5, were accumulated in  
unison and especially rapidly during spore germination.

Address Information:  Department of Plant Biology; University of  
Minnesota; Saint Paul, Minnesota 55108 USA
____________________________________________________

Robert Brambl
brambl at molbio.cbs.umn.edu