Linkage between oligomerization and DNA binding in Drosophila doublesex proteins

Area of Science:

• Molecular Biology
• Genetics
• Developmental Biology

Background:

• The doublesex gene in Drosophila melanogaster produces sex-specific proteins, DSXM (male) and DSXF (female).
• These proteins bind DNA and regulate transcription, with DSXM acting as a repressor and DSXF as an activator.
• Both proteins share a common DNA-binding domain (DBD) but possess distinct C-termini crucial for their function.

Purpose of the Study:

• To investigate the role of oligomerization domains, including the DBD and sex-specific C-termini, in DSX protein dimerization and DNA binding.
• To understand how these domains influence the apparent DNA binding affinity and binding cooperativity of DSXM and DSXF.

Main Methods:

• Electrophoretic mobility shift assays (EMSA) were employed to analyze protein-DNA interactions.
• The study compared the DNA binding affinities and dimerization constants of DBD dimers, DSXM dimers, and DSXF dimers.

Main Results:

• The intrinsic DNA binding affinities of DSXM and DSXF dimers were similar and slightly lower than DBD dimers.
• Dimerization affinities differed significantly, with full-length DSXM and DSXF dimers showing much stronger binding than DBD dimers.
• Full-length DSX dimers exhibited binding cooperativity on adjacent DNA sites, unlike DBD dimers, with distinct cooperativity levels for DSXM and DSXF.

Conclusions:

• Sex-specific C-terminal domains substantially enhance apparent DNA binding affinity through linked effects on dimerization.
• These domains also play a role in binding cooperativity, suggesting a complex regulatory mechanism dependent on DNA site arrangement.
• The findings highlight the importance of protein-protein interactions mediated by sex-specific domains in regulating gene expression during Drosophila development.