Abstract DNA polymerase β (polβ) is an essential en- zyme that has been shown to localize as discrete foci to the synaptonemal complex during meiosis in the mouse. To identify proteins that associate with polβ during mei- osis, we employed the yeast two-hybrid screen. Here we show that a multiple PDZ domain-containing protein, the glutamate receptor interacting protein 1 (GRIP1), inter- acts specifically with polβ. The PDZ domain-containing proteins, including GRIP1, act as scaffolds to promote rapid and localized biochemical events that require the interaction of multiple proteins. GRIP1 localizes to dis- crete foci on meiotic bivalents of both spermatocyte and oocyte nuclei, and colocalizes with polβ. Together, these findings provide evidence that GRIP1 interacts with polβ during meiosis. Our findings are consistent with the pos- sibility that GRIP1 acts as a scaffold to promote interac- tion between proteins that function during meiosis. Abbreviations polβ: DNA polymerase beta · GRIP1: glutamate receptor interacting protein 1 · SC: synaptonemal complex · AMPA: DL-α-amino-3- hydroxy-5-methyl-4-isoxazole propionic acid · MBP: maltose binding protein Introduction DNA polymerase β (polβ) is an essential M r 39,000 eu- karyotic enzyme that functions in base excision repair (BER) (Clairmont and Sweasy 1996; Sobol et al. 1996). This role is supported by the demonstration that homozy- gous deletion of polβ in a mouse embryonic cell line re- sults in sensitivity to methyl methane sulfonate and abol- ishes uracil DNA glycosylase-mediated BER in vitro (Sobol et al. 1996). DNA polymerase β is essential for development in that mice deleted of exons 1 and 2 of this gene die shortly after birth due to massive apoptosis of postmitotic neurons (Sugo et al. 2000). Several lines of evidence suggest that polβ functions during meiosis. DNA polymerase β is highly expressed in testis, with the highest levels observed in pachytene spermatocytes (Hubscher et al. 1977; Grippo et al. 1978; Hirose et al. 1989). During prophase I of meiosis, two discrete phases of DNA synthesis are observed. In zygo- nema, semi-conservative synthesis occurs, which is pro- posed to be associated with initial pairing and gene con- version. In pachynema, repair synthesis is observed, and probably occurs during the resolution and repair of re- combination intermediates (Carpenter 1981; Stern and Hotta 1987). This meiotic DNA synthesis is sensitive to concentrations of ddTTP that primarily inhibit polβ (Orlando et al. 1988). Although the timing and relative amounts of meiotic DNA synthesis are well character- ized, little is known about its enzymology in vivo (Stern and Hotta 1987). Our laboratory has recently shown that polβ localizes to discrete foci on meiotic bivalents dur- ing the zygotene and pachytene stages of prophase I (Plug et al. 1997a). Several other proteins with well characterized roles in DNA repair have also been local- ized to foci on meiotic chromosomes. These proteins include Mlh1, Rad51 and ATM (Ashley et al. 1995; Savitsky et al. 1995; Baker et al. 1996; Moens et al. 1997; Plug et al. 1997b; Barlow et al. 1998; Tarsounas et al. 1999). It has been proposed that these foci may actu- ally represent large multiprotein complexes containing the enzymatic machinery necessary for catalysis of mei- otic recombination (Carpenter 1979; Moens et al. 1998). To address the possibility that polβ may interact with other proteins during meiosis, we screened a mouse tes- tis cDNA library using the entire rat polβ cDNA se- quence as bait in a yeast two-hybrid system (Fields and Song 1989; Vojtek et al. 1997). Among the positive clones, we identified one that encoded a fragment of the Edited by: P. Moens A.S. Jonason · J.B. Sweasy ( ✉ ) Departments of Therapeutic Radiology and Genetics, Yale University School of Medicine, New Haven, CT 06520, USA e-mail: joann.sweasy@yale.edu S.M. Baker Division of Nutrition Sciences and Toxicology, University of California at Berkeley, Berkeley, CA 94720, USA Chromosoma (2001) 110:402–410 DOI 10.1007/s004120100165 ORIGINAL ARTICLE Alan S. Jonason · Sean M. Baker · Joann B. Sweasy Interaction of DNA polymerase β with GRIP1 during meiosis Received: 13 March 2001 / In revised form: 18 July 2001 / Accepted: 25 July 2001 / Published online: 12 September 2001 © Springer-Verlag 2001