Bioinformatic Prediction of an tRNA^Sec Gene Nested inside an Elongation Factor SelB Gene in Alphaproteobacteria

• Main Author: Takahito Mukai
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: International Journal of Molecular Sciences
• Subjects: genetic code; selenocysteine; non-coding RNA
• Online Access: https://www.mdpi.com/1422-0067/22/9/4605

In bacteria, selenocysteine (Sec) is incorporated into proteins via the recoding of a particular codon, the UGA stop codon in most cases. Sec-tRNA^Sec is delivered to the ribosome by the Sec-dedicated elongation factor SelB that also recognizes a Sec-insertion sequence element following the codon on the mRNA. Since the excess of SelB may lead to sequestration of Sec-tRNA^Sec under selenium deficiency or oxidative stress, the expression levels of SelB and tRNA^Sec should be regulated. In this bioinformatic study, I analyzed the Rhizobiales SelB species because they were annotated to have a non-canonical C-terminal extension. I found that the open reading frame (ORF) of diverse Alphaproteobacteria <i>selB</i> genes includes an entire tRNA^Sec sequence (<i>selC</i>) and overlaps with the start codon of the downstream ORF. A remnant tRNA^Sec sequence was found in the <i>Sinorhizobium meliloti</i><i>selB</i> genes whose products have a shorter C-terminal extension. Similar overlapping traits were found in Gammaproteobacteria and Nitrospirae. I hypothesized that once the tRNA^Sec moiety is folded and processed, the expression of the full-length SelB may be repressed. This is the first report on a nested tRNA gene inside a protein ORF in bacteria.