ADA3 - A GENE, IDENTIFIED BY RESISTANCE TO GAL4-VP16, WITH PROPERTIESSIMILAR TO AND DIFFERENT FROM THOSE OF ADA2

We describe the isolation of a yeast gene, ADA3, mutations in which pr event the toxicity of GALA-VP16 in vivo. Toxicity was previously propo sed to be due to the trapping of general transcription factors require d at RNA polymerase II promoters (S. L. Berger, B. Pina, N. Silverman, G. A. Marcus, J. Agapite, J. L. Regier, S. J. Triezenberg, and L. Gua rente, Cell 70:251-265, 1992). trans activation by VP16 as well as the acidic activation domain of GCN4 is reduced in the mutant. Other acti vation domains, such as those of GAL4 and HAP4, are only slightly affe cted in the mutant. This spectrum is similar to that observed for muta nts with lesions in ADA2, a gene proposed to encode a transcriptional adaptor. The ADA3 gene is not absolutely essential for cell growth, bu t gene disruption mutants grow slowly and are temperature sensitive. S trains doubly disrupted for ada2 and ada3 grow no more slowly than sin gle mutants, providing further evidence that these genes function in t he same pathway. Selection of initiation sites by the general transcri ptional machinery in vitro is altered in the ada3 mutant, providing a clue that ADA3 could be a novel general transcription factor involved in the response to acidic activators.