Genetic analysis of the Rad51D gene
Genetic analysis of the Rad51D gene.
The key event in recombination repair of DNA double strand breaks (DSB) is
the formation of the Rad51 nucleoprotein filament, which is necessary for the
homology search and exchange of DNA strands. An important role in the
regulation of the assembly, stabilization, and disassembly of Rad51 filaments
is played by the Rad51 paralogs — proteins structurally similar to Rad51.
Recently, an interest Rad51 paralogs has greatly increased due to their
significant role in carcinogenesis. Mammals have six paralogs of the Rad51:
Rad51B, Rad51C, Rad51D, XRCC2;, XRCC3 and the SWSAP1 (RadA homolog). The
Drosophila genome contains the Rad51 ortholog spnA and four Rad51 paralogs:
spnB (XRCC3 homolog), spnD (hRad51C), XRCC2 and Rad51D. However, the functions
of these proteins remain largely unclear.
The rad201G1 mutation (radiation sensitive 201) was isolated from
a natural population by its larval hypersensitivity to ionizing radiation
(Khromykh, Zakharow, 1981). Subsequently, the rad201G1 mutation was
extensively characterized genetically in respect of its effects on meiotic and
mitotic recombination, spontaneous and radiation-induced chromosome
aberrations, mutagenesis, radiation induced effects in oogenesis and in
the development. Here we show that the rad201G1 mutation is caused by
the insertion of the Opus retrotransposon at the 5 ’ untranslated region
of the Rad51D gene. In addition to the Opus insertion in the site
of mutation, the 'rad201G1' chromosome contains a number of nucleotide changes,
which cause K61E, V93A and Y108H subtitutions in the Rad51D and F50L in the
protein encoded by the overlapping CG42382 gene. We isolated spontaneous
reversions of the rad201 radiation sensitivity phenotype. All reversions
are associated with the loss of Opus, leaving the nucleotide
substitutions in Rad51D and CG42382 genes intact. In
the rad201G1 mutant embryos the Rad51D transcription is 30-fold
reduced by contrast with the wild type or revertants, while the level of
the CG42382 transcription does not differ . Thus, the rad201G1
mutation is a Rad51D allele. By contrast with the other studied members
of the Rad51 family in Drosophila, Rad51D mutant has a very weak spindle
phenotype which appears only with age. The results of the studies of genetic
interactions between Rad51D[rad201] and spn-A mutations will be
presented. A known genetic effects of the rad201G1 mutation will be
reviewed in a light of the fact that they reflect the functions of the
Drosophila Rad51D gene.
