title: Alteration of tRNA modification in eukaryotes: causes and consequences.
abstract: To evaluate the role of the modified nucleosides in tRNA function, especially their involvement in regulatory mechanisms of development, differentiation, or neoplastic transformation we use the following organisms: eubacteria, the slime mold D. discoideum, the topminnow Xiphophorus, and mice. Ribosylthymine, a common modified nucleoside at position 54 in tRNAs of prokaryotes and the major class of eukaryotic elongator tRNAs, is involved in the binding to the ribosomal A-site and is important for the proper functioning of tRNA during translation. Alterations in the extent of this modification occur early in the development of D. discoideum. The fully methylated species are found on polysomes, actively synthesizing protein. The partially methylated tRNAs accumulate in the nuclei, and might be involved in regulatory mechanisms at the transcriptional level. The Q base, a modified deazaguanine derivative, is present at position 34, the first position of the anticodon of tRNAAsn, tRNATyr, and tRNAHis. Alterations in the extent of this modification occur in corresponding tRNAs during the first minutes after the onset of development in D. discoideum and before final differentiation into spores, indicating that Q is important for developmental processes. Changes in the modification of G34 to Q34 in specific tRNAs of the melanophoric system of the topminnow Xiphophorus further support the view that Q is necessary in differentiation. In plasmacytomas and in Ehrlich ascites tumor cells of mice, the amount of unmodified G34 in corresponding tRNAs is correlated to the growth rate, density, or age of the tumor cells.
mesh_terms: D000818:Animals; D001483:Base Sequence; D004023:Dictyostelium / Q000502:physiology; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D009374:Neoplasms, Experimental / Q000378:metabolism; D009690:Nucleic Acid Conformation; D010954:Plasmacytoma / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity; D014158:Transcription, Genetic
chemical_list: D006147:Guanine; C019549:queuine; D012343:RNA, Transfer