Position effect on expression of dsd genes cloned onto multicopy plasmids

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The D-serine deaminase (dsd) system in Escherichia coli is regulated by positive control.
• Previous studies indicated complex regulatory mechanisms within this system.

Purpose of the Study:

• To investigate the in vivo and in vitro trans-activation capabilities of the D-serine deaminase regulatory gene (dsdC) in Escherichia coli.
• To reconcile conflicting results regarding the dominance of the dsdC+ gene in regulating dsd gene expression.

Main Methods:

• Utilized multicopy hybrid plasmids containing various components of the dsd system (dsdC+, dsdCO+A+, dsdC delta O+A+, dsdC+O+A+).
• Performed in vivo expression studies by examining the induction of chromosomal and plasmid-borne dsd loci.
• Employed an in vitro coupled transcription-translation system to assess the activity of synthesized and purified D-serine deaminase regulatory protein (dsdC+).

Main Results:

• Lack of trans-activation in vivo when dsdC+ was present on multicopy plasmids or when chromosomal dsdC+ regulated plasmid-borne fragments.
• High inducibility of the entire dsd system (dsdC+O+A+) on hybrid plasmids.
• Efficient in vitro activation of dsdA+ expression by both in vitro-synthesized and exogenously purified dsdC+ protein.

Conclusions:

• The D-serine deaminase regulatory protein (dsdC+) demonstrates potent trans-activation activity in vitro, but not in vivo under tested conditions with multicopy plasmids.
• Discrepancies between in vivo and in vitro results suggest complex regulatory interactions or limitations in the in vivo experimental setup.
• Further investigation is needed to fully elucidate the in vivo regulatory mechanisms of the D-serine deaminase system in Escherichia coli.