Positive regulation of the Drosophila melanogaster G6PD gene by a transposable element: its structure and function.

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Three high G6PD-activity mutants of D. melanogaster which have been found in a laboratory stock are characterized by two insertion sequences associated with the G6PD locus; one (Ins 1) is present just 5' to exon I and the other resides within an intron. The aim of the present project was to study the structure and function of the Ins 1 sequence. The following results were obtained: (1) The Ins 1 sequence consists of a core sequence flanked by a KP and KP' elements, and the sequence responsible for high G6PD activity may be the core sequence;(2) Cloning and sequencing data of the core sequence showed that this is another type of defective P elements(the internal sequence ranging from base 206 to base 2503 in the P element of p 25.1 is deleted); (3) The sequence spanning the junction of the 205th and the 2504th bases is unique to this particular type of P elements and may be capable of forming a palindrome in its central portion; (4) There is a protein in the nuclei of Canton S and mutant embryos that specifically binds to the core sequence; (5) The core sequence has a pair of DNase hypersensitive sites; (6) The transcription start site and the length of G6PD mRNA do not differ in wild-type and mutant stocks.Based on these findings, it was concluded that insertion of a particular type of defective P elements in front of the G6PD coding domain provides the G6PD gene with a site to which a nuclear protein probably of regulatory function can bind, and hence, without disturbing the normal transcription machinery, results in the acceleration of transcription.