Removal of an intron with unique 3' branch site creates an amino-terminal protein sequence directing the scERV1 gene product to mitochondria.

The yeast scERV1 gene is of special interest because it has a dual function in mitochondrial biogenesis and in the regulation of the cell cycle. The recent discovery that the yeast scERV1 gene has a structural and functional human homologue initiated a detailed comparison of the genes and their structures. In addition the homologous ALR (augmenter of liver regeneration) genes from rat and mouse have just been identified and it has been found that the mammalian proteins have a specific function in liver regeneration and in spermatogenesis. It now turns out that the organization of the 5' regions of these genes is much more complicated than expected. The latest research has discovered an additional intron in the 5' region of the mouse gene and possible amino-terminal extensions of the reading frames. In this work, reinvestigation of the 5' region of the yeast gene identifies a putative intron with an unusual 3' branch site. It is shown that a small intron of 83 nucleotides is present in this genomic region. Analysis of cDNA clones demonstrates that the intron is correctly removed from the messenger RNA and that therefore the unusual 3' branch site is probably functional. Furthermore, studies with antibodies directed against recombinant scERV1 protein demonstrate that the gene product is associated with mitochondria, in agreement with its involvement in mitochondrial biogenesis. Complementation experiments with mutants and different 5' deletions of the gene identify the corresponding promotor for transcription and the start codon for translation.