Genetic Evidence Links the ASTRA Protein Chaperone Component Tti2 to the SAGA Transcription Factor Tra1

摘要

is a 3744-residue component of the Saccharomyces cerevisiae SAGA, NuA4, and ASTRA complexes. contains essential C-terminal PI3K and FATC domains, but unlike other PIKK (phosphoinositide three-kinase–related kinase) family members, lacks kinase activity. To analyze functions of the FATC domain, we selected for suppressors of -F3744A, an allele that results in slow growth under numerous conditions of stress. Two alleles of , -F328S and -I336F, acted in a partially dominant fashion to suppress the growth-related phenotypes associated with -F3744A as well as its resulting defects in transcription. -F328S suppressed an additional FATC domain mutation (-L3733A), but not a mutation in the PI3K domain or deletions of SAGA or NuA4 components. We find eGFP-tagged distributed throughout the cell. is a component of the ASTRA complex, and in mammalian cells associates with molecular chaperones in complex with and . Consistent with this finding, levels are reduced in a strain with a temperature-sensitive allele of . Further agreeing with a possible role for in the folding or stabilization of href="http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000001141" data-ga-action="click_feat_suppl" ref="reftype=extlink&article-id=3389973&issue-id=211838&journal-id=301&FROM=Article%7CFront%20Matter&TO=External%7CLink%7CURI" target="_blank">Tra1, href="http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000001141" data-ga-action="click_feat_suppl" ref="reftype=extlink&article-id=3389973&issue-id=211838&journal-id=301&FROM=Article%7CFront%20Matter&TO=External%7CLink%7CURI" target="_blank">tra1-F3744A was mislocalized to the cytoplasm, particularly under conditions of stress. Since an intragenic mutation of href="http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000001141" data-ga-action="click_feat_suppl" ref="reftype=extlink&article-id=3389973&issue-id=211838&journal-id=301&FROM=Article%7CFront%20Matter&TO=External%7CLink%7CURI" target="_blank">tra1-R3590I also suppressed F3744A, we propose that href="http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000003897" data-ga-action="click_feat_suppl" ref="reftype=extlink&article-id=3389973&issue-id=211838&journal-id=301&FROM=Article%7CFront%20Matter&TO=External%7CLink%7CURI" target="_blank">Tti2 is required for the folding/stability of the C-terminal FATC and PI3K domains of href="http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000001141" data-ga-action="click_feat_suppl" ref="reftype=extlink&article-id=3389973&issue-id=211838&journal-id=301&FROM=Article%7CFront%20Matter&TO=External%7CLink%7CURI" target="_blank">Tra1 into their functionally active form.