Dictyostelium discoideum: a useful model system to evaluate the function of queuine and of the Q‐family of tRNAs

Abstract

(Dictyostelium discoideum)Wild-type strain Axenic strain Queuine supply Development tRNA modification

Characterisation of a Dictyostelium discoideum DNA fragment coding for a putative tRNAValGUU gene.

“…As source for the tRNA ligase a tRNA-free I00000 x g supernatant was used [32]. The aminoacylated tRNA was applied to a Sepharose column to which the elongation factor Tu (EF-Tu) from Escherichiu coli had been covalently bound [33].…”

Recognition of UAG termination codon by mammalian tyrosine tRNA containing 6-thioqueuine in the first position of the anticodon.

“…It would also be interesting to examine biological effects of 6-thioqueuine in other eukaryotic cells such as Dictyosterium discoideum and T etrahymena, since it is known that queuine is efficiently incorporated into tRNA of those cells when queuine is added in the culture medium (Ott et al, 1982;Kuchino et al, unpublished results).…”

Queuosine modification in tRNA and expression of the nitrate reductase in Escherichia coli.

“…Eubacteria and plants synthesize queuine de novo, whereas protists and mammals are supplied with queuine by nutrition or by the intestinal flora (Katze, 1982;Ott et al, 1982;Farkas, 1980). In eubacteria a precursor of queuine (pre-queuine) and in eukaryotes queuine, is inserted into the corresponding tRNAs by exchange with guanine 34 by specific tRNA-guanine transglycosylases (Okada et al, 1979; Katze and Farkas, 1979).…”

“…Axenic strains can be grown vegetatively as single amoebae in a well-defined medium in the absence of queuine. The addition of queuine to the growth medium causes a complete modification of the corresponding tRNAs (Ott et al, 1982). When amoebae lacking Q in tRNA are starved under unfavourable conditions they lose their ability to differentiate into stalk cells and spores, whereas amoebae sufficiently supplied with queuine will overcome this metabolic stress and undergo further development.…”

“…We therefore conclude that a Q-tRNA is involved in the expression of the gene of the nitrate dehydrogenase complex that oxidizes D(-)-lactate, independently of NAD, to pyruvate under anaerobic conditions. Queuine is synthesized de novo in eubacteria and plants, but it is an essential nutrient in the protozoon D. discoideum (Ott et al, 1982). In this respect it is of interest that nitrate respiration has been found in the inner mitochondrial membrane of protozoon Loxodes.…”