The Yeast Type I Topoisomerase Top3 Interacts with Sgsl, a DNA Helicase Homolog: a Potential Eukaryotic Reverse Gyrase

Abstract

We have previously shown that cells mutant for TOP3, a gene encoding a prokaryotic-like type I topoisomerase in Saccharomyces cerevisiae, display a pleiotropic phenotype including slow growth and genome instability. We identified a mutation, sgs1 (slow growth suppressor), that suppresses both the growth defect and the increased genomic instability of top3 mutants. Here we report the independent isolation of the SGS1 gene in a screen for proteins that interact with Top3. DNA sequence analysis reveals that the putative Sgs1 protein is highly homologous to the helicase encoded by the Escherichia coli recQ gene. These results imply that Sgs1 creates a deleterious topological substrate that Top3 preferentially resolves. The interaction of the Sgs1 helicase homolog and the Top3 topoisomerase is reminiscent of the recently described structure of reverse gyrase from Sulfolobus acidocaldarius, in which a type I DNA topoisomerase and a helicase-like domain are fused in a single polypeptide.

Topoisomerase III is required for accurate DNA replication and chromosome segregation in Schizosaccharomyces pombe

“…The S.cerevisiae sgs1 mutant was isolated as a suppressor of the slow growth phenotype of the top3 deletion mutant (4). SGS1 is a member of the RecQ helicase family which includes ®ssion yeast rqh1 + and human BLM, WRN and REQL4 helicases which are implicated in Bloom's, Werner's and Rothmund±Thomson syndromes, respectively (5±8).…”

Phase separated ribosome nascent chain complexes paused in translation are capable to continue expression of proteins playing role in genotoxic stress response upon DNA damage

“…It is important to note that the stress response cannot be managed by the ubiquitous and continuous expression of certain effectors. For example, concerning the context of the DNA damage response, overexpression of Sgs1, a DNA helicase involved in double-strand DNA break repair, is toxic in yeast (Gangloff et al, 1994; Sinclair et al,1997), or overexpression of the Rad1-Rad10 subunits of Nef1 leads to gross chromosome rearrangements (Hwang et al, 2005). The clear advantage of their delayed completed translation could be that the gene products - required for DNA repair albeit toxic would be expressed in an active form only when the DNA damage appears, avoiding the detrimental effects of unnecessary or excess expression.…”

Saccharomyces cerevisiae as a Model System for Eukaryotic Cell Biology, from Cell Cycle Control to DNA Damage Response

“…Next, the second end of the DSB is engaged by Rad52 in a process called second end capture, which results in the formation of a double Holliday junction [ 184 , 185 , 186 ]. The double Holliday junction is resolved by the combined action of the helicase Sgs1, the topoisomerase Top3 or the Mus81/Mms4 complex resulting in crossover and non-crossover products [ 187 , 188 , 189 ]. In crossover products the part of the homologous strand used as a template is exchanged.…”