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Substrate Recognition of the Pseudouridine
Synthase RluA
Todd M. Greco and Eugene Mueller
Department of Chemistry and Biochemistry
The pseudouridine synthases catalyze the isomerization of uridine
in RNA to its C-glycoside isomer. This isomerization is the most
prevalent post-transcriptional modification of RNA, with pseudouridine
being found in all organisms, occurring in tRNA, rRNA, snRNA, and snoRNA
[Grosjean, H. and Benne, R. (1998) Modification and Editing of RNA, ASM
Press, Washington, DC]. Previous work involving molecular recognition
of tRNA by pseudouridine synthases has shown that the T-arm stem-loop (a
17-mer) from E. coli tRNA was an excellent substrate for TruB [Santi,
D.V., Gu, X., Yu, M., and Ivanetich, K. (1998) Biochemistry 37, 339-343].
We now examine the substrate specificity of E. coli RluA that isomerizes
both U32 in the anticodon loop of tRNA and U746 in 23S rRNA, which are
found in identical loop sequences (UUGAAAA) but have different stem sequences.
When RluA was incubated with the appropriate stem loops from tRNAPhe and
23S rRNA, total digestion and HPLC analysis showed that pseudouridine was
formed. In the case of the anticodon stem-loop, the intact product
stem-loop (with pseudouridine) was resolved from substrate (with U).
The analysis showed quantitative conversion to product. A new assay
was developed to utilize this separation of intact substrate and product
stem-loop to compare the kinetics of the "mini-substrates" to full length
tRNA. |