Yeast Meiosis-Specific Protein Hop1 Binds to G4 DNA and Promotes Its Formation

Abstract

DNA molecules containing stretches of contiguous guanine residues can assume a stable configuration in which planar quartets of guanine residues joined by Hoogsteen pairing appear in a stacked array. This conformation, called G4 DNA, has been implicated in several aspects of chromosome behavior including immunoglobulin gene rearrangements, promoter activation, and telomere maintenance. Moreover, the ability of the yeast SEP1 gene product to cleave DNA in a G4-DNA-dependent fashion, as well as that of the SGS1 gene product to unwind G4 DNA, has suggested a crucial role for this structure in meiotic synapsis and recombination. Here, we demonstrate that the HOP1 gene product, which plays a crucial role in the formation of synaptonemal complex in Saccharomyces cerevisiae, binds robustly to G4 DNA. The apparent dissociation constant for interaction with G4 DNA is 2 × 10⁻¹⁰, indicative of binding that is about 1,000-fold stronger than to normal duplex DNA. Oligonucleotides of appropriate sequence bound Hop1 protein maximally if the DNA was first subjected to conditions favoring the formation of G4 DNA. Furthermore, incubation of unfolded oligonucleotides with Hop1 led to their transformation into G4 DNA. Methylation interference experiments confirmed that modifications blocking G4 DNA formation inhibit Hop1 binding. In contrast, neither bacterial RecA proteins that preferentially interact with GT-rich DNA nor histone H1 bound strongly to G4 DNA or induced its formation. These findings implicate specific interactions of Hop1 protein with G4 DNA in the pathway to chromosomal synapsis and recombination in meiosis.

ACKNOWLEDGMENTS

We thank Mary Kironmai, Moreshwar Vaze, and R. Ajay Kumar for generous gifts of purified Hop1 and RecA proteins used in the initial stages of this study.

This research was supported by a fellowship from the American Cancer Society, Yamagiwa-Yoshida fellowship (administered by UICC, Geneva, Switzerland), a grant from the Department of Science and Technology, New Delhi, to K.M., and an NIH grant (GM-18541) to B.B.