GAL4/UAS system

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The GAL4-UAS system is a biochemical method used to study gene expression and function in organisms such as the fruit fly. It has proved to be a very powerful technique for studying the expression of genes.^[1] The system has two parts: the GAL4 gene, encoding the yeast transcription activator protein Gal4, and the UAS (Upstream Activation Sequence), a short section of the promoter region, to which Gal4 specifically binds to activate gene transcription.

Gal4 is a modular protein consisting broadly of a DNA-binding domain and an activation domain. The UAS to which Gal4 binds is CGG-N₁₁-CCG, where N can be any base^[2]. Although Gal4 is a yeast protein not normally present in other organisms it has been shown to work as a transcription factor in a variety of organisms such as Drosophila^[3], and human cells^[4], highlighting that the same mechanisms for gene expression have been conserved over the course of evolution.

For study in Drosophila, the GAL4 gene is placed under the control of a native gene promoter, or driver gene, while the UAS controls expression of a target gene. GAL4 is then only expressed in cells where the driver gene is usually active. In turn, Gal4 should only activate gene transcription where a UAS has been introduced. For example, by fusing a gene encoding a visible marker such as GFP (Green Fluorescent Protein) the expression pattern of the driver genes can be determined. GAL4 and the UAS are very useful for studying gene expression in Drosophila as they are not normally present and their expression does not interfere with other processes in the cell. However, some research has indicated that over-expression of GAL4 in Drosophila can have side-effects, probably relating to immune and stress responses to what is essentially an alien protein.^[5]

The GAL4-UAS system has also been employed to study gene expression in organisms besides Drosophila, such as the African clawed frog Xenopus^[6] and zebrafish.^[7]

The GAL4/UAS system is also utilized in Two-Hybrid Screening, a method of identifying interactions between two proteins or a protein with DNA.

References

1. ^ Duffy, JB. GAL4 system in Drosophila: A fly geneticist's Swiss army knife. Genesis. 2002 32:1-15
2. ^ Campbell RN et al., 2008. Metabolic control of transcription: Paradigms and lessons from Saccharomyces cerevsiae. Biochem J 414(2):177-87
3. ^ Fischer JA, 1988. GAL4 activates transcription in Drosophila. Nature 332(6167):853-6
4. ^ Webster N et al., 1988. The yeast UASG is a transcription enhancer in human HeLa cells in the presence of the GAL4 trans-activator. Cell 52(2):169-78
5. ^ Liu Y and Lehman M, 2008. A genomic response to the yeast transcription factor GAL4 in Drosophila. Fly (Austin) 2(2) (Epub ahead of print)
6. ^ Hartley KO et al., 2002. Targeted gene expression in transgenic Xenopus using the binary Gal4-UAS system. Proc Natl Acad Sci UAS 99(3):1377-82
7. ^ Davison JA et al., 2007. Transactivation from Gal4-VP16 transgenic insertions for tissue-specific cell labeling and ablation in zebrafish. Developmental Biology 304(2):811-24