A Truncated P Element is Inserted in the Transcribed Region of the Cu, Zn Sod Gene of an Sod “Null” Strain of Drosophila Melanogaster

Abstract

The decreased Cu, Zn SOD activity (less than 5%) in a “null” SOD^CAI Drosophila melanogaster strain isolated in our laboratory is due to the insertion of a truncated P element into the transcribed region of the Cu, Zn SOD gene.

Using a cDNA Cu, Zn SOD probe from a wild type D. melanoguster (F allele) we isolated an EcoRl Cu, Zn SOD clone from an EMBL3 genomic library of the SOD^CAI strain, subcloned it, restriction-mapped and partially sequenced it. The 2.5 kb clone consists of a wild-type 1.84 kb EcoRl fragment containing the Cu, Zn SOD gene previously isolated in our laboratory, with an insertion of 0.68 kb derived (by an internal deletion) from an autonomous. 2.9 kbP element. The insertion starts 21 bp upstream from the coding sequence and causes an 8 bp target site duplication characteristic of P elements.

A point mutation in the second exon results in a replacement of Asn by Lys at position 96. confirming that the mature protein encoded by the SOC^CAI is the same one encoded by the S allele, commonly found in natural populations. The diminished expression of SOD^CAI allele is most possibly due to a reduction of the rate of transcription attributable to the inscrtion of the P element.

Key Words:

• Null mutation
• DNA transposition
• transcription
• fitness
• population genetics.