The 19S proteasome regulatory particle plays a critical role in cellular proteolysis. However, recent reports have demonstrated that 19S proteins play a nonproteolytic role in nucleotide excision repair and transcription elongation. We show by chromatin immunoprecipitation assays that proteins comprising the 19S complex are recruited to the GAL1-10 promoter by the Gal4 transactivator upon induction with galactose. This recruited complex does not contain proteins from the 20S proteolytic particle and includes a subset of the 19S proteins. This subset is also specifically retained from an extract by the Gal4 activation domain. These data indicate that in vivo, the base of the 19S complex functions independently of the larger complex and plays a direct, nonproteolytic role in RNA polymerase II transcription.

Coenzyme Q(10) (CoQ(10)) plays a pivotal role in oxidative phosphorylation (OXPHOS) in that it distributes electrons between the various dehydrogenases and the cytochrome segments of the respiratory chain. Primary coenzyme Q(10) deficiency represents a clinically heterogeneous condition suggestive of genetic heterogeneity, and several disease genes have been previously identified. The CABC1 gene, also called COQ8 or ADCK3, is the human homolog of the yeast ABC1/COQ8 gene, one of the numerous genes involved in the ubiquinone biosynthesis pathway. The exact function of the Abc1/Coq8 protein is as yet unknown, but this protein is classified as a putative protein kinase. We report here CABC1 gene mutations in four ubiquinone-deficient patients in three distinct families. These patients presented a similar progressive neurological disorder with cerebellar atrophy and seizures. In all cases, enzymological studies pointed to ubiquinone deficiency. CoQ(10) deficiency was confirmed by decreased content of ubiquinone in muscle. Various missense mutations (R213W, G272V, G272D, and E551K) modifying highly conserved amino acids of the protein and a 1 bp frameshift insertion c.[1812_1813insG] were identified. The missense mutations were introduced into the yeast ABC1/COQ8 gene and expressed in a Saccharomyces cerevisiae strain in which the ABC1/COQ8 gene was deleted. All the missense mutations resulted in a respiratory phenotype with no or decreased growth on glycerol medium and a severe reduction in ubiquinone synthesis, demonstrating that these mutations alter the protein function.

Coenzyme Q 10 (CoQ 10 ) plays a pivotal role in oxidative phosphorylation (OXPHOS), as it distributes electrons among the various dehydrogenases and the cytochrome segments of the respiratory chain. We have identified 2 novel inborn errors of CoQ 10 biosynthesis in 2 distinct families. In both cases, enzymologic studies showed that quinone-dependent OXPHOS activities were in the range of the lowest control values, while OXPHOS enzyme activities were normal. CoQ 10 deficiency was confirmed by restoration of normal OXPHOS activities after addition of quinone. A genome-wide search for homozygosity in family 1 identified a region of chromosome 10 encompassing the gene prenyldiphosphate synthase, subunit 1 (PDSS1), which encodes the human ortholog of the yeast COQ1 gene, a key enzyme of CoQ 10 synthesis. Sequencing of PDSS1 identified a homozygous nucleotide substitution modifying a conserved amino acid of the protein (D308E). In the second family, direct sequencing of OH-benzoate polyprenyltransferase (COQ2), the human ortholog of the yeast COQ2 gene, identified a single base pair frameshift deletion resulting in a premature stop codon (c.1198delT, N401fsX415). Transformation of yeast Δcoq1 and Δcoq2 strains by mutant yeast COQ1 and mutant human COQ2 genes, respectively, resulted in defective growth on respiratory medium, indicating that these mutations are indeed the cause of OXPHOS deficiency.