During meiosis, after DNA replication, the pairing of chromosomes involves four copies of each chromatid, which synapse together before recombination takes place. Certain short guanine-rich motifs in single-stranded DNA self-recognize and associate in physiological salt to make four-stranded structures in which the strands run in a parallel fashion. Such four-stranded structures, named G4-DNA, are able to crosslink four Watson-Crick duplexes. Such guanine-rich sequences have been found in immunoglobulin switch regions and in the telomeres of chromosomes. It is possible that this self-recognition of G-rich motifs in DNA is used to bring together the four chromatids that must synapse in meiosis, where a series of different G4-DNA-forming regions along the entire length of a chromosome might serve as an identification pattern for pairing. G4-DNA crosslinks may also be used to align chromosomes in mitosis and in the formation of polytene chromosomes. This project will test the hypothesis that G4-DNA-forming regions serve as identification signals for chromosome matching. Anti-G4- DNA antibodies will be used to detect G4-DNA in chromosomes during meiotic pairing. Crosslinks between chromosomes involved in meiotic pairing will be isolated to investigate whether their sequences are such that they can form G4-DNA structures. Such G4- DNA-forming elements and their surrounding sequences will be cloned, and the engagement of guanines into G4-DNA in vivo will be demonstrated by in vivo dimethyl sulfate methylation experiments. The cell may control the formation of G4-DNA at special times in the cell cycle by synthesizing G4-DNA-binding proteins and special DNA melting proteins. Both proteins that recognize G4-DNA and melting proteins that relax the DNA structure in specific regions, in which one strand is unusually G-rich, will be sought. By binding the C-rich strand, such melting proteins would free the G- rich regions to seek each other out from chromatid to chromatid to make crosslinks to bring together four duplexes. The significance of the G4-DNA hypothesis is that it provides an understanding of how chromosome pairing is accomplished throughout eukaryotic organisms and explains why four chromatids are involved in recombination.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
1R01GM041895-01
Application #
3300361
Study Section
Genetics Study Section (GEN)
Project Start
1989-04-01
Project End
1992-03-31
Budget Start
1989-04-01
Budget End
1990-03-31
Support Year
1
Fiscal Year
1989
Total Cost
Indirect Cost
Name
Harvard University
Department
Type
Schools of Arts and Sciences
DUNS #
071723621
City
Cambridge
State
MA
Country
United States
Zip Code
02138
Frantz, J D; Gilbert, W (1995) A yeast gene product, G4p2, with a specific affinity for quadruplex nucleic acids. J Biol Chem 270:9413-9
Frantz, J D; Gilbert, W (1995) A novel yeast gene product, G4p1, with a specific affinity for quadruplex nucleic acids. J Biol Chem 270:20692-7
Liu, Z; Frantz, J D; Gilbert, W et al. (1993) Identification and characterization of a nuclease activity specific for G4 tetrastranded DNA. Proc Natl Acad Sci U S A 90:3157-61
Sen, D; Gilbert, W (1992) Novel DNA superstructures formed by telomere-like oligomers. Biochemistry 31:65-70