| Abstract: | Incorporation of 5-bromodeoxyuridine (5-BUdR) into nuclear DNA severely interrupts the life cycle of Dictyostelium discoideum after the first generation of growth. Loose cellular aggregates are then formed, but no spore or stalk cells are detectable and no other morphological transformations are observed. The perturbation of gene expression in the life cycle has been studied at the protein level by two-dimensional gel electrophoresis after pulse labelling with 35S-methionine and also by changes in the patterns of polysomal messenger RNA population. The latter was monitored by hybridisation studies using specific cDNA probes for “vegetative” and “18 hr” messenger RNAs. In the presence of 5-BUdR major anomalies in polypeptide synthesis were observed after the loose aggregation stage. Some vegetative polypeptides, including actin, which are normally abundant only during growth to the aggregation stage, are oversynthesised during the period 12-24 hr after starvation. In this same interval the normal decline in the abundance of vegetative mRNA species was not observed. In marked contrast virtually half the normal “18 hr-specific polypeptides” were poorly synthesised. Likewise, the normal increase in abundance of the corresponding “18 hr-specific” poly A + RNA species in the polysomes did not occur. No major alteration in the timing of the appearance of new macromolecules during the cell cycle was observed in spite of extensive modification of gene expression by the incorporation of 5-BUdR into genomic DNA. |
