#Microinject the embryo with DNA coding for transposase and a plasmid with the reporter gene and transposase recognition sequences (and often the E. coli reporter gene and origin of replication, etc.).
#Random transposition occurs, inserting the reporter gene randomly. The insertion tends to occur near actively transcribed genes, as this is where the chromatin structure is loosest, so the DNA is most accessible.
#Grow flies and cross to remove genetic variation between the cells of the organism (see above).
#Look for flies expressing the reporter gene. These have experienced a successful transposition, so can be investigated to determine the phenotype due to mutation of existing genes.
Possible mutations:
#Insertion in a translated region => hybrid protein/truncated protein. Usually causes loss of protein function, although more complex effects are seen.
#Insertion in an intron => altered splicing pattern/splicing failure. Usually results in protein truncation or the production of inactive mis-spliced products, although more complex effects are common.
#Insertion in 5 (the sequence that will become the mRNA 5 UTR) untranslated region => truncation of transcript. Usually results in failure of the mRNA to contain a 5' cap, leading to less efficient translation.
#Insertion in promoter => reduction/complete loss of expression. Always results in greatly reduced protein production levels. The most useful type of insertion for analysis due to the simplicity of the situation.
#Insertion between promoter and upstream enhancers => loss of enhancer function/hijack of enhancer function for reporter gene.† Generally reduces the level of protein specificity to cell type, although complex effects are often seen.