title: Saccharomyces cerevisiae Hrq1 helicase activity is affected by the sequence but not the length of single-stranded DNA.
abstract: Mutations in the human RecQ4 DNA helicase are associated with three different diseases characterized by genomic instability. To gain insight into how RecQ4 dysfunction leads to these pathologies, several groups have used the Saccharomyces cerevisiae RecQ4 homolog Hrq1 as an experimental model. Hrq1 displays many of the same functions as RecQ4 in vivo and in vitro. However, there is some disagreement in the literature about the effects of single-stranded DNA (ssDNA) length on Hrq1 helicase activity and the ability of Hrq1 to anneal complementary ssDNA oligonucleotides into duplex DNA. Here, we present a side-by-side comparison of Hrq1 and RecQ4 helicase activity, demonstrating that in both cases, long random-sequence 3' ssDNA tails inhibit DNA unwinding in vitro in a length-dependent manner. This appears to be due to the formation of secondary structures in the random-sequence ssDNA because Hrq1 preferentially unwound poly(dT)-tailed forks independent of ssDNA length. Further, RecQ4 is capable of ssDNA strand annealing and annealing-dependent strand exchange, but Hrq1 lacks these activities. These results establish the importance of DNA sequence in Hrq1 helicase activity, and the absence of Hrq1 strand annealing activity explains the previously identified discrepancies between S. cerevisiae Hrq1 and human RecQ4.
authors.affiliation: Molecular and Cellular Biochemistry Department, 212 South Hawthorne Drive, Simon Hall MSB1, Room 405B, Indiana University, Bloomington, IN 47405, USA. Electronic address: codroger@indiana.edu.
authors.forename: Cody M
authors.initials: CM
authors.lastname: Rogers
authors.affiliation: Molecular and Cellular Biochemistry Department, 212 South Hawthorne Drive, Simon Hall MSB1, Room 405B, Indiana University, Bloomington, IN 47405, USA. Electronic address: bochman@indiana.edu.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Bochman
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D004277:DNA, Single-Stranded / Q000737:chemistry* / Q000235:genetics*; D004789:Enzyme Activation / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011485:Protein Binding; D053484:RecQ Helicases / Q000737:chemistry* / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics*; D013045:Species Specificity; D013329:Structure-Activity Relationship
chemical_list: D004277:DNA, Single-Stranded; D029701:Saccharomyces cerevisiae Proteins; C579040:Hrq1 protein, S cerevisiae; C506731:RECQL4 protein, human; D053484:RecQ Helicases
keywords: DNA helicase; Hrq1; RecQ; RecQ4; Saccharomyces cerevisiae