Characterization and transcription analysis of a cloned sequence derived from a major developmentally regulated mRNA of D. discoideum.

The plasmid pDd 812 contains a portion of a poly(A)+ RNA sequence isolated from developing cells of the cellular slime mold Dictyostelium discoideum (Williams and Lloyd, 1979). The poly(A)+ RNA complementary to this plasmid shows an increase in concentration during the first 4 hr of development followed by a decrease in concentration during the following 4 hr. This RNA is very abundant after 3-4 hr of development, constituting at least 2% of the poly(A)+ RNA population. In this study, we demonstrate that this poly(A)+ RNA is an mRNA sequence by translating the RNA complementary to pDd 812 in a heterologous system. The mRNA directs the synthesis of a major polypeptide of 33,000 daltons and a minor polypeptide of 31,000 daltons. We have used the plasmid DNA immobilized on filters to analyze the transcription of this RNA sequence in isolated nuclei. The amount of transcript synthesized in nuclei isolated at various stages of development which was complementary to pDd 812 changed in the same way as did the cytoplasmic concentration of this RNA--that is, maximal transcription occurred after 3-4 hr of development. Because this result was observed using labeling periods as short as 5 min, we believe that this change is unlikely to reflect a change in the rate of processing of RNA. We interpret these results to indicate that, at least in part, the control of the synthesis of this RNA is at the level of gene transcription.