Reduced Aminoacylation of Asparagine-Transfer RNA Early in the Developmental Cycle ofDictyostelium discoideum:Modification Pattern and Possible Significance of the Uncharged Isoacceptor tRNA₃^Asn

Abstract

Changes in the pattern of isoacceptors of tRNA Asn and alterations in modification of the guanine residue 34, the first position of the anticodon of tRNA Asn , have been observed in eukaryotes during differentiation. We use Dictyostelium discoideum as a model system to elucidate the possible involvement of tRNA Asn in developmental processes.Vegetative amoebae were induced to undergo developmental transition by nutrient starvation. Since amino acid starvation alone is a specific stimulus initiating development and unacylated tRNAs might be involved in control mechanisms of protein synthesis, the level of aminoacylation of tRNA Asn isoacceptors has been investigated.As early as two minutes after the onset of development, the aminoacylation of tRNA Asn specifically was reduced to about 30%, whereas at the same time 10 other tRNA species were found to be charged normally, i.e. to 70-100%. One of the two major isoacceptors, tRNA Asn , was completely deacylated, whereas the other one, tRNA Asn , accounted for the residual aminoacylation. Analyses of the modified nucleosides of highly purified tRNA Asn and tRNA Asn respectively, show that both isoacceptors are identical in their modification patterns except for the modification at the first position of the anticodon: tRNA Asn comprises queuine (Q),7-[(4,5-czs-dihydroxy-2-cyclopenten-1 -ylamino)methyl]-7-deazaguanine, whereas tRNA Asn contains guanine.

The role of queuine in the aminoacylation of mammalian aspartate transfer RNAs

“…The importance of Q, however, was clearly shown in the case of Asn Dictysteliwn discoidewn (30), where G-tRNA was specifically present during developmental transition of vegetative amobae caused by nutrient starvation. G-tRNA was completely deacylated in vivo, while Q-tRNAAs was aminoacylated (also see 25).…”

Queuine Deficiency and Restoration in Dictyostelium discoideum and Related Early Developmental Changes

“…tRNAs with G in place of Q accumulate in foetal and regenerating rat liver and in a variety of animal tumours (Okada et al, Kersten, 1982). Germ-free mice, fed on a defined diet, do not synthesize queuine de novo, indicating that the modification is derived from nutrition or from the intestinal flora (Farkas, 1980; Reyniers et a!., 1981).We have shown that in Dictyostelium discoideum the extent of Q modification in the Q family of tRNAs changes during development and depends on the environmental conditions (Kersten, 1982;Dingermann et al, 1981 ; Ott et al, 1982). Non-axenic strains of the slime mould are Ahhreriurion : Q. queuosine ( 7 4 ((4.5-cis-dihydroxy-2-cyclopenten-1 -yl)-amino)-methyl)-7-deazaguanosine].…”

“…We have shown that in Dictyostelium discoideum the extent of Q modification in the Q family of tRNAs changes during development and depends on the environmental conditions (Kersten, 1982;Dingermann et al, 1981 ; Ott et al, 1982). Non-axenic strains of the slime mould are Ahhreriurion : Q. queuosine ( 7 4 ((4.5-cis-dihydroxy-2-cyclopenten-1 -yl)-amino)-methyl)-7-deazaguanosine].…”