Drosophila MUS312 interacts with the nucleotide excision repair endonuclease MEI-9 to generate meiotic crossovers

Abstract

MEI-9 is the Drosophila homolog of the human structure-specific DNA endonuclease XPF. Like XPF, MEI-9 functions in nucleotide excision repair and interstrand crosslink repair. MEI-9 is also required to generate meiotic crossovers, in a function thought to be associated with resolution of Holliday junction intermediates. We report here the identification of MUS312, a protein that physically interacts with MEI-9. We show that mutations in mus312 elicit a meiotic phenotype identical to that of mei-9 mutants. A missense mutation in mei-9 that disrupts the MEI-9-MUS312 interaction abolishes the meiotic function of mei-9 but does not affect the DNA repair functions of mei-9. We propose that MUS312 facilitates resolution of meiotic Holliday junction intermediates by MEI-9.

Fig. 1

Survival of mei-9 and mus312 mutants after treatment with DNA damaging agents. Percent survival is given relative to wild-type controls (heterozygous siblings; see Experimental Procedures for details). Bars indicate standard deviation of at least two independent experiments. The allele mei-9^A2 is a protein and genetic null, whereas mei-9¹² is a separation-of-function allele (see text); mus312 experiments were done with mus312^D1/ mus312^Z1973 compound heterozygotes. A. UV irradiation. B and D. Nitrogen mustard added to the medium. C. Methyl methanesulfonate added to the medium.

Fig. 2

A. Molecular map of mus312 and the interaction with MEI-9. A schematic of the genomic architecture of mus312 (CG8601) is shown. Each box represents an exon, and filled regions designate protein coding sequences. The bar above the map indicates the region contained in the yeast two hybrid clone that interacts with MEI-9 (without the intron). Asterisks represent potential nuclear localization signals. B. Interaction between MUS312 and MEI-9 in nuclear extracts (see Experimental Procedures for details). Lane 1 is GST alone; lanes 2 and 3 are GST-MUS312^1-387. The sample in lane 3 was treated with DNAseI prior to washing. C. Sequence of mei-9¹² allele. The sequence surrounding the mei-9¹² substitution is shown for Drosophila MEI-9 (residues 296 through 317) and human XPF (residues 306 through 328). D. Interaction between MUS312, MEI-9, and MEI-9¹² in a yeast two hybrid system. Colonies containing pGBD:MEI-9 (upper) or pGBD:MEI-9¹² (lower) and pACT2 vector, pGAD10:ERCC1, or pGAD10:MUS312 were streaked onto medium lacking threonine and leucine (to select for the presence of the two plasmids) and containing (+) or lacking (−) histidine. Growth on medium lacking histidine is indicative of an interaction between the fusion proteins. The MEI-9, MEI-9¹², and ERCC1 fusions were full-length; the MUS312 fusion contained the interaction domain mapping to residues 61-303.