# Defining the methanogenic SECIS element in vivo by targeted mutagenesis

## TL;DR

This paper identifies the functional structure of SECIS elements in archaea and reveals how they enable selenocysteine incorporation into proteins.

## Contribution

The study defines the minimal SECIS element in Methanococcus maripaludis using targeted mutagenesis and identifies key structural and functional features.

## Key findings

- The minimal functional SECIS element was defined through targeted mutagenesis.
- Two conserved adenines in the SECIS element are likely involved in interactions with Sec recoding machinery.
- SECIS elements in the 5'-untranslated region can be repositioned near the UGA codon for efficient selenocysteine insertion.

## Abstract

In all domains of life, Archaea, Eukarya and Bacteria, the unusual amino acid selenocysteine (Sec) is co-translationally incorporated into proteins by recoding a UGA stop codon to a sense codon. A secondary structure on the mRNA, the selenocysteine insertion sequence (SECIS), is required, but its position, secondary structure and binding partner(s) are not conserved across the tree of life. Thus far, the nature of archaeal SECIS elements has been derived mainly from sequence analyses. A recently developed in vivo reporter system was used to study the structure–function relationships of SECIS elements in Methanococcus maripaludis. Through targeted mutagenesis, we defined the minimal functional SECIS element, the parts of the SECIS where structure and not the identity of the bases are relevant for function, and identified two conserved -and invariant- adenines that are most likely to interact with the other factor(s) of the Sec recoding machinery. Finally, we demonstrated the functionality of SECIS elements in the 5`-untranslated region of the mRNA and identified a potential mechanism of SECIS repositioning in the vicinity of the UGA for efficient selenocysteine insertion.