Sequencing of chromosome I of Saccharomyces cerevisiae: analysis of the 42 kbp SPO7-CENI-CDC15 region

Mcp3 is a novel mitochondrial outer membrane protein that follows a unique IMP-dependent biogenesis pathway

Mitochondria are separated from the remainder of the eukaryotic cell by the mitochondrial outer membrane (MOM). The MOM plays an important role in different transport processes like lipid trafficking and protein import. In yeast, the ER-mitochondria encounter structure (ERMES) has a central, but poorly defined role in both activities. To understand the functions of the ERMES, we searched for suppressors of the deficiency of one of its components, Mdm10, and identified a novel mitochondrial protein that we named Mdm10 complementing protein 3 (Mcp3). Mcp3 partially rescues a variety of ERMES-related phenotypes. We further demonstrate that Mcp3 is an integral protein of the MOM that follows a unique import pathway. It is recognized initially by the import receptor Tom70 and then crosses the MOM via the translocase of the outer membrane. Mcp3 is next relayed to the TIM23 translocase at the inner membrane, gets processed by the inner membrane peptidase (IMP) and finally integrates into the MOM. Hence, Mcp3 follows a novel biogenesis route where a MOM protein is processed by a peptidase of the inner membrane.

A novel HSP70 gene of Schizosaccharomyces pombe that confers K-252a resistance

A new gene encoding a heat shock protein 70 family protein of Schizosaccharomyces pombe (Sp), named sks2+, was cloned as a weak suppressor for the K-252a-sensitive mutation, ucm1. The nucleotide sequence of sks2+ revealed an open reading frame of a 613-amino-acid (aa) protein. The deduced aa sequence of sks2+ showed significant homology with Saccharomyces cerevisiae (Sc) Ssb1p and Ssb2p responsible for protein synthesis by non-organelle-localized ribosomes, as well as with other proteins of the HSP70 family. The cells lacking the functional sks2+ gene were viable and showed no increased sensitivity to K-252a but grew slowly with an elongated morphology. These results suggest that the sks2+ gene product plays a role in the cell cycle progression and is able to confer drug resistance in a multicopy state.

DNA sequence analysis of the VPH1-SNF2 region on chromosome XV of Saccharomyces cerevisiae

The nucleotide sequence of a 37 000 base pair region from the left arm of chromosome XV of Saccharomyces cerevisiae has been determined and analysed. This region contains 21 open reading frames (ORFs) coding for proteins of more than 100 amino acids. Six ORFs correspond to the genes PAC1, VPH1, MOD5, CAP20, ORF1 and SNF2 already described. Eight ORFs show some similarities to known genes from yeast and other organisms. They include genes coding for serine/threonine protein kinases, a multidrug resistance family homologue, a protein related to dihydrofolate reductase, a cluster of heat shock-like proteins and a gene coding for an enzyme related to protein disulfide isomerase. Finally seven ORFs do not show any similarities with a known gene. In addition we found a new ala-tRNA (UGC) gene located next to a sigma sequence.

A Drosophila hsp70 gene contains long, antiparallel, coupled open reading frames (LAC ORFs) conserved in homologous loci

A clone isolated from a Drosophila auraria heat-shock cDNA library presents two long, antiparallel, coupled (LAC) open reading frames (ORFs). One strand ORF is 1,929 nucleotides long and exhibits great identity (87.5% at the nucleotide level and 94% at the amino acid level) with the hsp70 gene copies of D. melanogaster, while the second strand ORF, in antiparallel in-frame register arrangement, is 1,839 nucleotides long and exhibits 32% identity with a putative, recently identified, NAD(+)-dependent glutamate dehydrogenase (NAD(+)-GDH). The overlap of the two ORFs is 1,824 nucleotides long. Computational analysis shows that this LAC ORF arrangement is conserved in other hsp70 loci in a wide range of organisms, raising questions about possible evolutionary benefits of such a peculiar genomic organization.