SUMMARY: The modified deazaguanosine derivative queuosine (Q) is found in the first position of the anticodon in the Q-family of tRNAs of eubacteria and eukaryotes. The Q-base, queuine, is inserted into tRNA in exchange for guanine. Myxamoebae of cannot synthesize queuine , but obtain it from bacteria, their natural food supply. When grown on bacteria, is almost fully modified with respect to Q, whereas the corresponding tRNAs from axenic strains, due to queuine limitation in axenic media, contain submolar amounts of Q. Queuine does not affect growth rate, but accelerates development and stimulates spore germination. To establish whether changes might be caused early in the developmental cycle by an insufficient supply of queuine, vegetative amoebae of the strain AX-2 were induced by starvation to develop in suspension culture. Q deficiency in tRNA was rectified by the addition of queuine to the starvation buffer at a concentration of 10 M. During the first 12 h, when the cells acquired aggregation competence, restoration of queuine caused (i) an increase in binding of cAMP to its surface receptors, especially to the low-affinity binding site, and (ii) characteristic changes in the time course of the synthesis of distinct proteins in response to queuine as judged from the pattern of labelled proteins separated by two-dimensional gel electrophoresis.


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