Analysis of mRNA levels for developmentally regulated prespore specific glutamine synthetase in Dictyostelium...

The enzyme glutamine synthetase (GS) of Dictyostelium discoideum is developmentally regulated, preferentially localized in prespore cells and is likely to play an important role in controlling the levels of ammonia, a known morphogen, in this organism. To further investigate the regulation of GS, a portion of the GS gene was isolated and used as a probe to examine the changes in GS mRNA throughout development and the level of GS mRNA in the two precursor cell types. The amino acid sequence of the cloned DNA fragment isolated is highly homologous to other eukaryotic GS genes. DNA blot analysis demonstrated that the GS gene exists as a single copy in D. discoideum. Analysis of RNA indicated that there is a single 1.7 kb GS transcript that increased during development to peak at the initial stages of culmination. Furthermore, GS mRNA was highly localized in prespore cells, which is consistent with a proposed source-sink model for ammonia assimilation in this organism.