| 6440121 |
Van Buul CP, Hamersma M, Visser W, Van Knippenberg PH: Partial methylation of two adjacent adenosines in ribosomes from Euglena gracilis chloroplasts suggests evolutionary loss of an intermediate stage in the methyl-transfer reaction. Nucleic Acids Res. 1984 Dec 11;12(23):9205-8.
Bacterial, cytoplasmic and organellar ribosomes from a wide phylogenetic spectrum of organisms have a characteristic m6 (2) Am6 (2) A structure near the 3' end of the RNA of the small ribosomal subunit (SSU). We have studied one of the few exceptions to this extremely conserved post-transcriptionally modified sequence, i.e. dimethylation of only one of the two A's in chloroplasts from Euglena gracilis. It was established that only the A closest to the 5' end is dimethylated, the other one being unmodified. The methylation reaction was studied in vitro using ribosomes from a kasugamycin resistant mutant (ksgA) of Escherichia coli and purified methyl-transferase. Using limited amounts of the methyl donor S-adenosylmethionine (SAM) a partial level of methylation (50% of control) was attained. It is shown that in this case the 3' proximal A is dimethylated while the other is not. This suggests that dimethylation takes place in two successive stages. Apparently in E. gracilis chloroplasts the first stage of methylation does not occur. |
31(0,1,1,1) |