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Title: Alternate routes to mnm 5 s 2 U synthesis in Gram-positive bacteria
The wobble bases of tRNAs that decode split codons are often heavily modified. In bacteria, tRNAGlu, Gln, Aspcontains a variety of xnm5s2U derivatives. The synthesis pathway for these modifications is complex and fully elucidated only in a handful of organisms, including the Gram-negativeEscherichia coliK12 model. Despite the ubiquitous presence of mnm5s2U modification, genomic analysis shows the absence ofmnmCorthologous genes, suggesting the occurrence of alternate biosynthetic schemes for the conversion of cmnm5s2U to mnm5s2U. Using a combination of comparative genomics and genetic studies, a member of the YtqA subgroup of the radical Sam superfamily was found to be involved in the synthesis of mnm5s2U in bothBacillus subtilisandStreptococcus mutans. This protein, renamed MnmL, is encoded in an operon with the recently discovered MnmM methylase involved in the methylation of the pathway intermediate nm5s2U into mnm5s2U inB. subtilis. Analysis of tRNA modifications of bothS. mutansandStreptococcus pneumoniaeshows that growth conditions and genetic backgrounds influence the ratios of pathway intermediates owing to regulatory loops that are not yet understood. The MnmLM pathway is widespread along the bacterial tree, with some phyla, such as Bacilli, relying exclusively on these two enzymes. Although mechanistic details of these newly discovered components are not fully resolved, the occurrence of fusion proteins, alternate arrangements of biosynthetic components, and loss of biosynthetic branches provide examples of biosynthetic diversity to retain a conserved tRNA modification in Nature.IMPORTANCEThe xnm5s2U modifications found in several tRNAs at the wobble base position are widespread in bacteria where they have an important role in decoding efficiency and accuracy. This work identifies a novel enzyme (MnmL) that is a member of a subgroup of the very versatile radical SAM superfamily and is involved in the synthesis of mnm5s2U in several Gram-positive bacteria, including human pathogens. This is another novel example of a non-orthologous displacement in the field of tRNA modification synthesis, showing how different solutions evolve to retain U34 tRNA modifications.  more » « less
Award ID(s):
1716535
PAR ID:
10567881
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ;
Editor(s):
Henkin, Tina M
Publisher / Repository:
American Society for Microbiology
Date Published:
Journal Name:
Journal of Bacteriology
Volume:
206
Issue:
4
ISSN:
0021-9193
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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