ABSTRACT: 23S ribosomal RNA (rRNA) of Escherichia coli 50S large ribosome subunit contains 26 post-transcriptionally modified nucleosides. Here, we determine the extent of modifications in the 35S and 45S large subunit intermediates, accumulating in cells expressing the helicase inactive DbpA protein, R331A, and the native 50S large subunit. The modifications we characterized are nine pseudouridines, 3-methylpseudouridine, 2-methyladenine, and 5-hydroxycytosine. These modifications were detected using 1-cyclohexyl-(2-morpholinoethyl)carbodiimide metho-p-toluene sulfonate (CMCT) treatment followed by alkaline treatment. In addition, KMnO4 treatment of 23S rRNA was employed to detect 5-hydroxycytosine modification. CMCT and KMnO4 treatment produce chemical changes in modified nucleotides that cause reverse transcriptase misincorporations and deletions, which were detected employing next generation sequencing. Our results show that seven uridines to pseudouridine isomerizations and the 2-methyladenosine modification are present both in the 35S and 45S to similar extents as in the 50S. Hence, the enzymes that perform these modifications, namely RluF, RluB, RlmN, RluA, RluC, and RluA, have already acted in the intermediates. While two uridines to pseudouridines isomerizations, the 3-methylpseudouridine, and 5-hydroxycytosine modifications are significantly less present in the 35S and 45S as compared to the 50S. Therefore, the enzymes that perform these modifications, RluD, RlmH, and RlhA, are in the process of modifying the 35S, and 45S or these enzymes act during the later stages of ribosome assembly. Our study employs a novel high throughput and single nucleotide resolution technique for detection of 2-methyladenine and two novel high throughput and single nucleotide resolution technique for detection of 5-hydroxycytosine.
