Department of Genetics and Microbiology, University of Georgia, Athens, Georgia, USA.
Mol Microbiol. 2022 Jul;118(1-2):30-46. doi: 10.1111/mmi.14949. Epub 2022 Jun 13.
Despite significant progress in understanding the diversity of tRNA processing pathways in Escherichia coli, the mechanism for the maturation of tRNAs encoded within the rRNA operons has not received much attention. Here, we show that the Glu2, Ile1, and Ala1B tRNAs, encoded by 10 genes located between the 16S and 23S rRNAs in the seven rRNA operons, are matured via a RNase E-independent processing pathway that utilizes at least six different enzymes. It has been shown that the Glu2 and Ile1-Ala1B pre-tRNAs released by initial RNase III cleavages of the 30S primary rRNA transcripts retain extended 5'-leader (35-139 nt) and 3'-trailer (166-185 nt) sequences. However, the 5' maturation of the tRNAs by RNase P is inhibited until the trailer sequences are shortened to 1-4 nucleotides, initially by a second RNase III cleavage at 31-42 nucleotides downstream of the CCA determinant followed by exonucleolytic trimming. The RNase III cleaved Glu2 and Ile1-Ala1B trailer fragments are degraded via PAP I- dependent exonucleolytic decay. Compared to the six previously characterized tRNA processing pathways, maturation of the Glu2, Ile1, and Ala1B tRNAs is considerably more complex and appears to be distinct from what occurs in Gram-positive bacteria.
尽管在理解大肠杆菌 tRNA 加工途径的多样性方面取得了重大进展，但 rRNA 操纵子内编码的 tRNA 的成熟机制并未受到太多关注。在这里，我们表明，Glu2、Ile1 和 Ala1B tRNA 是由位于七个 rRNA 操纵子中 16S 和 23S rRNA 之间的 10 个基因编码的，它们通过一种不依赖于 RNase E 的加工途径成熟，该途径至少利用了六种不同的酶。已经表明，Glu2 和 Ile1-Ala1B 前 tRNA 通过 30S 初级 rRNA 转录物的初始 RNase III 切割释放出来，保留了延伸的 5'-leader（35-139nt）和 3'-trailer（166-185nt）序列。然而，直到 trailer 序列缩短到 1-4 个核苷酸，RNase P 对 tRNA 的 5' 成熟才会受到抑制，最初是通过在 CCA 决定因素下游 31-42 个核苷酸处的第二个 RNase III 切割，然后进行外切核酸酶修剪。RNase III 切割的 Glu2 和 Ile1-Ala1B trailer 片段通过依赖于 PAP I 的外切核酸酶降解。与之前鉴定的六种 tRNA 加工途径相比，Glu2、Ile1 和 Ala1B tRNA 的成熟过程要复杂得多，似乎与革兰氏阳性菌中的情况不同。
