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The Saccharomyces cerevisiae ribosomal protein rp5l is encoded by two interchangeable genes, RPSIA and RPSIB. We altered the RPS1 gene dose by creating deletions of the RPS1A or RPSJB genes or both. Deletions of both genes led to spore inviability, indicating that rp5l is an essential ribosomal protein. From single deletion studies in haploid cells, we concluded that there was no intergenic dosage compensation at the level of mRNA abundaince or mRNA utilization (translational efficiency), although phenotypic analysis had previously indicated a small compensation effect on growth rate. Similarly, deletions in diploid strains indicated that no strong mechanisms exist for intragenic dosage compensation; in all cases, a decreased dose of RPS1 genes was characterized by a slow growth phenotype. A decreased dose of RPSI genes also led to insufficient amounts of 40S ribosomal subunits, as evidenced by a dramatic accumulation of excess 60S ribosomal subunits. We conclude that inhibition of 40S synthesis had little or no effect on the synthesis of the 60S subunit components. Addition of extra copies of rpSl genes led to extra rp5l protein synthesis. The additional rp5l protein was rapidly degraded. We propose that rp5l and perhaps mnany ribosomal proteins are normally oversynthesized, but the unassembled excess is degraded, and that the apparent compensation seen in haploids, i.e., the fact that the growth rate of mutant strains is less depressed than the actual reduction in mRNA, is a consequence of this excess which is spared from proteolysis under this circumstance.The Saccharomyces cerevisiae ribosome is composed of four rRNA species and approximately 70 ribosomal proteins present in stoichiometric amounts. The accumulation of the rRNA and protein components is coordinately regulated in response to the nutritional requirements of the cell. As a result, little or no free ribosomal proteins are present in vivo (for a review, see reference 21). In an effort to understand the mechanisms that govern this regulation, the genes for many of the yeast ribosomal proteins have been cloned (2,6,23). From these initial studies, the following facts emerged: there is almost no clustering in the organization of the ribosomal protein genes (24), and many but not all of them are represented by more than one copy (6). Since the mRNAs for various ribosomal proteins have been determined to be present in roughly equimolar amounts and have very similar half lives (14), it follows that there should be quantitative differences in the transcription of single copy and multiple copy genes if the latter are all active.Ribosomal URA3 gene and the 3' end of RPSB was gel purified. The same plasmid was cut with EcoRI and HincII, and. the fragment containing the 5' end of RPSB was gel purified. Both fragments were ligated to pUC9 (Pharmacia P-L Biochemicals) cut with EcoRI and HindIll. Yeast strains. The yeast strains used and their characteristics were as follows: DBY745 a ura3-52 adel-100 leu2(2-3,112) (3); HR125-5D a ura3-52 trpl leu2(2-3,112) his...

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The ability of dendritic cells to activate both naive and effector T cells in vitro and in vivo can be enhanced with the use of poxvirus vectors that potentiate the hyperexpression of a triad of costimulatory molecules. Use of either rF-TRICOM or rV-TRICOM vectors significantly improved the efficacy of dendritic cells in priming specific immune responses. These studies have implications in vaccine strategies for both cancer and infectious diseases.