Chloroplast tRNAAsp: nucleotide sequence and variation of in vivo levels during plastid maturation

Abstract

Two chloroplast tRNA(Asp) species from barely were purified by chromatography on benzoylated DEAE-cellulose and sequenced. They differ in the modification at position 34, where queuosine (Q) is present in one of the species. The same chromatographic procedure yielded only one tRNA(Glu) species, corroborating the assumption that the same tRNA(Glu) species participates in both protein and chlorophyll biosynthesis. The level of tRNA(Glu) remains unchanged after light treatment of etiolated seedlings, whereas the amount of tRNA(Asp) decreases to about 50% relative to the level of dark-grown plants.

Diet-dependent depletion of queuosine in tRNAs in Caenorhabditis elegans does not lead to a developmental block

“…Apart from the known exceptions of yeast, Thermus thermophilus, mycoplasma and mycobacteria, Q is found in organisms from all major divisions of life (Kasai et al 1975;Katze et al 1982;Reader et al 2004). The tRNA Asp from mitochondria (Randerath et al 1984) and chloroplast (Schon et al 1992) are also known to possess Q. The biosynthesis of Q in eubacteria involves a series of reactions (Reader et al 2004).…”

Overview of tRNA Modifications in Chloroplasts

“…In contrast to the aforementioned modifications, plastidial tRNAs reading G 1 NN codons do not possess modifications of A 37 [55,75,76], with the exception of tRNA-Asp [77] which has not been identified. Indeed, according to nucleotide pairing rules [7], cytosine strictly pairs with guanosine, which is sufficient to prevent frameshifts and mispairing of N 1 :C 36 .…”

“…Interestingly, there is evidence pointing to the presence of queuine (Q) instead of G 34 in certain plant tissues or under particular growth conditions [77,89,90]. To corroborate these observations, two queuine tRNA-ribosyltransferases were identified in the nuclear genome of C. reinhardtii and one of them (Cre12.g558400) showed a high probability of being transferred to the chloroplast.…”

“…This enzyme acts on all tRNAs harboring a U 35 in the second anticodon position (His, Asn, Asp and Tyr). Nonetheless, queuine has not been found in the tRNA of His and Asn and is only present in specific conditions for Asp and Tyr in plants [77,89,90]. One explanation for this is that most eukaryotes, including C. reinhardtii, are not able to synthesize queuine.…”

“…Namely, Um 34 , cmnm 5 U 34 /cmnm 5 s 2 U 34 [55,64,75] and U* 34 (* represents an unidentified modification) [57,65,76] for uridine; Inosine (I) replacing the adenosine 34 in the arginine tRNA-I 34 CG [55,65,108]; Cytosine modification into k 2 C 34 for the isoleucine tRNA-k 2 C 34 AU [56]. Queuosine is represented in dashed lines because of the lack of solid evidence [77,89,90], thus remaining hypothetical. In theory, this modification affects tRNA of the type G 34 U 35 N (His, Asn, Asp and Tyr).…”