MSL-1 plays a central role in assembly of the MSL complex which mediates dosage compensation in Drosophila melanogaster : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Genetics at Massey University, Palmerston North, New Zealand

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Massey University
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Dosage compensation in Drosophila melanogaster is achieved by a twofold increase of transcription of X-linked genes in males. This involves the binding of four proteins, MSL-1, MSL-2, MSL-3 and MLE (collectively known as the MSLs) which are believed to act as a multi-protein complex, to hundreds of sites along the length of the X chromosome. MOF, a putative histonc acetyl transferase, is thought to be also associated with MSLs and plays a role in hypertrascription of X-linked genes. Overexpression of either a C-terminal or N-terminal domain of MSL-1 leads to male-specific lethality which is probably due to association with other MSLs to form a non-functional complex. One aim of this study was to identify whether any known MSLs and/or unknown protein binds with the C-terminal domain of MSL-1. A second aim was to further define the domain of MSL-1 which interacts to MSL-2. Initial attempts to identify the protein which interacts the C-terminal domain of MSL-1 by either genetics analysis or co-immunoprecipitation were inconclusive. Thus, an alternative approach of affinity chromatography of epitope-tagged MSL-1/MSL-complex was followed. Transgenic flies which express either a FLAG-tagged N-terminal region of MSL-1 or FLAG tagged C-terminal domain following heat shock were generated. These lines were crossed with other transgenic lines to co-express the MSL-1 domain with Either MSL-2, MSL-3, MLE or MOF. FLAG affinity chromatography of protein extracts prepared from these flies showed that MSL-2 co-purifies with the N-terminal domain of MSL-1 (aa 85 - 263), whereas MOF and MSL-3 co-purify with the C-terminal domain of MSL-1 (aa 705 - 1039). MLE docs not appear to associate with either region of MSL-1. Further, the C-terminal domain of MSL-1 also bound specifically to a glutathione S-transferase-MOF fusion protein. Co-expression of MSL-2 rescued males from the lethal effect which was caused by overexpression of the N-terminal domain of MSL-1. However, co-expression of either or both MOF and MSL-3 with the C-terminal domain of MSL-1 did not improve male viability. This suggests that additional factors may bind to the FC/MOF/MSL-3 complex. Finally, MLE also bound to GST-MOF fusion protein, suggesting a direct interaction between MLE and MOF. These findings suggest that MSL-1 plays a central in assembly of the MSL multi-protein complex that is required to achieve dosage compensation.
Drosophila melanogaster, Genetics, Gene expression