Abstract
IMP1 encodes a subunit of the mitochondrial inner membrane peptidase responsible for the proteolytic processing of cytochrome oxidase subunit 2 (Cox2) and cytochromeb 2 (Cytb2). The molecular defect in animp1 mutation and the characterisation of a high-copy-number suppressor is described. A delection of the suppressor region causes respiration deficiency. The DNA sequence revealed three very small overlap** ORFs. Constructs which carried termination codons within the ORFs or lacked ATG initiation codons still retained complementing activity on a high-copy-number plasmid. Nevertheless, the possibility that the suppressor acts at DNA or RNA level could be excluded. Subcloning of the ORFs, complementation analysis in low-copy-number plasmids and transcript map** identified the 222 bp ORF as the suppressor gene designatedSOM1. TheSOM1 gene is transcribed into a 375 bp polyadenylated RNA and the deduced amino acid sequence predicts a small protein of 8.4 kDa with no significant sequence similarity to known proteins. In thesom1 deletion mutant, proteolytic processing of the Cox2 precursor is prevented and Cytb2 is strongly reduced.SOM1 represents a new small gene which encodes a novel factor that is essential for the correct function of the Imp1 peptidase and/or the protein sorting machinery.
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Communicated by C. P. Hollenberg
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Esser, K., Pratje, E. & Michaelis, G. SOM 1, a small new gene required for mitochondrial inner membrane peptidase function inSaccharomyces cerevisiae . Molec. Gen. Genet. 252, 437–445 (1996). https://doi.org/10.1007/BF02173009
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DOI: https://doi.org/10.1007/BF02173009