Synthesis of transfer ribonucleic acids with uridine or 2'-O-methylribothymidine at position 54 in developing Dictyostelium discoideum

In amoebae of Dictyostelium discoideum the ribothymidine (rT) content of tRNA is 0.9 mol%, but decreases progressively during development into spores. To elucidate which nucleosides replace rT at position 54 in developmental tRNA we have characterized 'vegetative' and 'developmental' tRNAs from the slime mould. Specific tRNAs were separated by two-dimensional gel electrophoresis. During early developmental stages, all tRNA species that could be separated by this method were newly synthesized. A new tRNA with uridine in place of rT and having an electrophoretic mobility similar to 'vegetative' tRNAAsn was detected during the early preaggregation stage. This 'development' tRNA was also extracted from purified polysomes. When development proceeds from preaggregation to postaggregation, tRNAs accumulate with 2'-O-methylribothymidine in place of rT. We suggest that these developmental tRNAs are important for the synthesis of specific developmental proteins.