The dose-, LET-, and gene-dependent patterns of intragenic DNA changes underlying recessive visible mutations at the autosomal gene cinnabar of Drosophila melanogaster

Abstract

Sequence analysis of 2 spontaneous, 26 γ-ray- and 10 neutron/neutron + γ-ray-induced cn gene/point mutants was performed. One spontaneous mutant had the entire maternal сn¹ sequence studied (4644 bp, full gene conversion). The second mutant contained cluster of DNA changes consisting of a partial gene conversion (tract length of 1087 bp), as well as an extended deletion (47 bp) and one single-base substitution in exon 2. Almost the same spectra of DNA changes in γ-ray- and neutron/neutron + γ-ray-induced cn mutants made it possible to unite them into one group of 36 radiation-induced mutants. Among the 36 mutants studied, 5 mutants (13.9 %) did’t have any DNA changes within the studied sequence of the cn genomic region. The 31 remaining mutants contained 36 DNA changes. There were 3 (8.3 %) single-base substitutions, 2 (5.5 %) frameshifts or indels 1–3-bp long, 14 (38.9 %) extended deletions of 5–21 bp in length, 12 (33.3 %) gene conversion events, 2 (5.5 %) large insertion (∼ 6.0 kb) of unidentified origin, and 1 (2.8 %) large (640 bp) deletion, 1 (2.8 %) extended insertion (8 bp), 1 (2.8 %) insertion/duplication (505 bp). Among 12 gene conversion events, there were 7 full and 5 partial events. The tract length in the mutants with partial conversion varies from 44 to 2247 bp. According to literature data such DNA changes as gene conversion, extended deletions, and indels must be the products of homologous recombination, single-strand annealing, and non-homologous ends joining repair pathways, respectively. We propose that the initial DNA lesions for DNA changes are different types of DNA double-strand breaks (DSB): (i) complex DSBs, (ii) less complex DSBs, and (iii) simple DSBs. Comparing the spectrum of DNA changes in the cn gene/point mutants with that in black one, it is important to note that the ratio of DNA changes in various genomic regions may be different.