An extended Escherichia coli "selenocysteine insertion sequence" (SECIS) as a multifunctional RNA structure

Area of Science:

• Molecular Biology
• Genetics
• RNA Structure and Function

Background:

• The genetic code exhibits flexibility, allowing for alternative interpretations of codons.
• The UGA codon typically signals translation termination but can direct selenocysteine incorporation.
• Selenocysteine incorporation relies on a cis-acting mRNA element, the selenocysteine insertion sequence (SECIS), forming a stem-loop structure.

Purpose of the Study:

• To investigate the minimal requirements and functional elements of the E. coli SECIS.
• To understand the role of specific SECIS nucleotides and their interaction with proteins.
• To explore additional functions of the fdhF SECIS, particularly in preventing UGA readthrough.

Main Methods:

• Analysis of the minimal E. coli SECIS structure and its necessity for selenocysteine incorporation.
• Investigation of a bulged U residue within the SECIS upper stem-loop and its interaction with SelB.
• Characterization of an extended fdhF SECIS for its role in preventing UGA readthrough under selenium deficiency.

Main Results:

• In E. coli, a 17-nucleotide upper-stem and loop region of the SECIS is sufficient for selenocysteine incorporation when properly positioned.
• A bulged U residue in the SECIS upper stem-loop is crucial for selenocysteine incorporation, interacting with SelB.
• The fdhF SECIS contains elements that prevent UGA readthrough during selenium deficiency, involving a downstream C residue and an upstream region coding for arginine and valine.

Conclusions:

• The E. coli SECIS is a multifunctional RNA element.
• It can direct selenocysteine incorporation or, under selenium deficiency, prevent UGA readthrough, acting as a switch for translational machinery.
• A model of the E. coli fdhF SECIS highlights three functional elements contributing to its dual role.