Sites of P element insertion and structures of P element deletions in the 5' region of Drosophila melanogaster RpII215.

Abstract

Several P element insertion and deletion mutations near the 5' end of Drosophila melanogaster RplI215 have been examined by nucleotide sequencing. Two different sites of P element insertion, approximately 90 nucleotides apart, have been detected in this region of the gene. Therefore, including an additional site of P element insertion within the coding region, there are at least three distinct sites of P element insertion at RplI215. Both 5' sites are within a noncoding portion of transcribed sequences. The sequences of four revertants of one P element insertion mutation (D50) indicate that the P element is either precisely deleted or internally deleted to restore RpII215 activity. Partial internal deletions of the P element result in different RpII215 activity levels, which appear to depend on the specific sequences that remain after excision.In Drosophila melanogaster, the transposable P elements are responsible for some if not all of the traits associated with the P-M hybrid dysgenesis syndrome, including increased frequencies of mutation, male recombination, chromosome rearrangement, and female sterility (27; reviewed in references 3 and 7). Hybrid dysgenesis is observed in the progeny of interstrain crosses between male flies from the wild (P strains) and females from laboratory stocks (M strains) but not in the reciprocal cross. P strains harbor multiple copies of P elements dispersed throughout their genomes, whereas M strains lack functional P elements (27). Dysgenic crosses result in germ line alterations due to transposition and excision of P elements and P-mediated chromosome rearrangement.The molecular structures of several P elements have been characterized by O'Hare and Rubin (23). The elements in this family are heterogeneous in size, the largest, known as P factor, being 2.9 kilobases (kb) long. The smaller P elements appear to arise by internal deletions of the complete P factor. A 31-base-pair (bp) inverted repeat, apparently required for transposition (15), is found at the ends of the P element, and 8 bp of chromosomal DNA are duplicated at the insertion site. A transposase, encoded by the 2.9-kb P factor, is necessary for movement of these elements (19,25,26,32). The smaller P elements are defective for transposase activity and depend on transposase provided in trans for mobilization.Reversions of mutations caused by P element insertion occur at high frequencies (10-2 to 10-3) (6,8,9,27,34) and are associated with excision of P elements (5, 27, 29). For example, reversions of a P element insertion mutation at the white locus were shown to be precise excisions of the P element and one copy of the 8-bp duplication (23). Presumably, only precise excision events could be detected as reversions since the insertion is located in coding sequences of white. On the other hand, genomic Southern analysis of several revertants of a P element insertion at the 5' end of the RpII215 locus (29,34) (4,12,35), although the subunit encoded at the locus was not identified in these studies. This RpII gene was clo...

Molecular analysis of hybrid dysgenesis-induced derivatives of a P-element allele at the vg locus.

“…The vg2-4-Rev derivative has three bases (GAT; data not shown) inserted at the internal deletion end point, while vg2'-7 has two bases inserted at the breakpoint (GG; data not shown). This type of alteration has been observed before (24,30). The genomic PstI site is at position -139 (data not shown), while the genomic SstI site is at position +62.…”

“…The secondary mutants are often revertants, but they may also be more extreme derivatives of the original allele. They have been extensively studied at the rudimentary (34), RP11215 (30,35), and yellow loci (3). Secondary mutants have been shown to be due to either precise or imprecise P-element excisions (3,24,30,34,35), internal deletions within the resident P element (4,30,34), deletion of DNA adjacent to the resident P element (4,34), or inversions with a breakpoint within the P element (7,34).…”

apterous, a gene required for imaginal disc development in Drosophila encodes a member of the LIM family of developmental regulatory proteins.

“…Sarov and D. Segal, in prep.). The production of hypomorphic alleles by excision of P elements has been documented previously (e.g., Searles et al 1986). These investigators …”

Novel DNA structures resulting from dTam3 excision in tobacco

“…On the other hand, internal excision is a wellknown phenomenon of a transposable element structurally related to Ac and Tam3: the Pdement from Drosophila [24,30]. A recent report presents evidence for the suggestion that internal excision of a non-autonomous P-element only occurs when no wild-type locus is present (in the case of strains homozygous for a P-element insertion [ 5]).…”

“…However, a contra-1003 diction with the P-element system comes from the analyses of re-integration. In the P-element system there still are new insertions in the genome while an internal excision is registered in the empty donor site [5,30]. Of the six plants we analysed only one plant had a re-integrated nonintact dTam3 dement.…”