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The S. pombe RPB8 gene, encoding for a subunit common to all three RNA polymerases, has been isolated by its ability to overcome the effects of the gcn2 mutation of S. cerevisiae. In wild type cells, when total protein synthesis is reduced under amino-acid or purine- starvation conditions, the Gcn2 protein kinase phosphorylates the alpha-subunit of the translation initiation factor eIF-2, resulting in the increased synthesis of the Gcn4 protein. Several lines of genetic evidence suggest that the S. pombe Rpb8 subunit affects the translational machinery in S. cerevisiae by competing with the endogenous subunit for the assembly of the RNA polymerase III complex. Mutated cloned S. cerevisiae RPB8 genes which mimic the effects of their S. pombe homologue allow for direct genetic and biochemical in vivo and in vitro tests of interacting molecules with Rpb8 which will reveal its function.
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