Department of Life Science, College of Science, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan.
Int J Mol Sci. 2021 Apr 27;22(9):4605. doi: 10.3390/ijms22094605.
In bacteria, selenocysteine (Sec) is incorporated into proteins via the recoding of a particular codon, the UGA stop codon in most cases. Sec-tRNA 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 under selenium deficiency or oxidative stress, the expression levels of SelB and tRNA 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 genes includes an entire tRNA sequence () and overlaps with the start codon of the downstream ORF. A remnant tRNA sequence was found in the genes whose products have a shorter C-terminal extension. Similar overlapping traits were found in Gammaproteobacteria and Nitrospirae. I hypothesized that once the tRNA 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.
在细菌中，硒代半胱氨酸（Sec）通过特定密码子的重编码掺入蛋白质，在大多数情况下是 UGA 终止密码子。Sec-tRNA 由 Sec 专用延伸因子 SelB 递送至核糖体，SelB 还识别 mRNA 上密码子后的 Sec 插入序列元件。由于 SelB 的过量可能导致硒缺乏或氧化应激下 Sec-tRNA 的隔离，因此 SelB 和 tRNA 的表达水平应该受到调节。在这项生物信息学研究中，我分析了根瘤菌科 SelB 物种，因为它们被注释为具有非典型的 C 末端延伸。我发现，不同的α变形菌基因的开放阅读框（ORF）包含整个 tRNA 序列（），并与下游 ORF 的起始密码子重叠。在产物具有较短 C 末端延伸的基因中发现了残留的 tRNA 序列。在γ变形菌和硝化螺旋菌中也发现了类似的重叠特征。我假设一旦 tRNA 部分折叠和加工，全长 SelB 的表达可能会受到抑制。这是细菌中蛋白质 ORF 内嵌套 tRNA 基因的第一个报告。
