Subject(s)
Drosophila Proteins , Drosophila melanogaster/genetics , Insect Hormones/genetics , Nerve Tissue Proteins/genetics , Nuclear Proteins/genetics , Point Mutation , Retroelements , Animals , Base Sequence , Gene Amplification , Homeodomain Proteins , Male , Microfilament Proteins , Molecular Sequence Data , Oligodeoxyribonucleotides , Restriction Mapping , Transcription FactorsABSTRACT
The genetically unstable Mutator Strain of D. melanogaster is characterised by a high frequency of spontaneous mutations and their reversions. Three forked mutants were obtained independently and several reversions arose spontaneously with frequency of 10(-3)-10(-4). The sites of integration and excision of the gypsy retrotransposon were analysed by Southern blot analysis and sequencing of PCR fragments. In all cases gypsy had inserted at the end of the third exon of the major transcript of the forked gene, causing the duplication of TCCA target sequence. All the reversions resulted from precise excision of the gypsy. A double mutant containing ct6 and f1, caused by gypsy insertions into untranslated regions of the corresponding genes, was constructed. Two spontaneous ct6f+ revertants as well as one ct+f1 revertant were obtained from this line. Sequence analysis of gypsy integration and excision sites revealed that in all cases gypsy excision was also precise. These experiments constitute the first demonstration of precise excision of LTR-containing elements from their host genomes.
Subject(s)
Drosophila melanogaster/genetics , Mutation/genetics , Retroelements/physiology , Animals , Base Sequence , Crosses, Genetic , Exons/genetics , Female , Genes, Insect/genetics , Male , Molecular Sequence Data , Mutagenesis , Sequence Analysis, DNA , X ChromosomeABSTRACT
A previously described system of a Drosophila melanogaster mutative strain (MS), which originates from a stable strain (SS), is characterized by genetic instability caused by transposition of the retrotransposon gypsy. New unstable strains were obtained by microinjections of the gypsy transposable copy into SS embryos. In situ hybridization experiments revealed amplification and active transposition of gypsy in SS derivatives. At the same time, introduction of the gypsy transposable copy into another stable strain (208) did not lead to appearance of genetic instability. Genetic instability in the MS system is apparently induced by a combination of two factors: the presence of a gypsy transposable copy and mutation(s) in the gene(s) regulating its transpositions.
