Two divergently transcribed genes of Dictyostelium discoideum are cyclic AMP-inducible and coregulated during development.

Abstract

The cysteine proteinase 1 (CP1) gene of Dictyostelium discoideum encodes a developmentally regulated sulfhydryl proteinase. We characterized the DNA sequences upstream of the CP1 gene and found a second developmentally regulated gene, which we term DG17. The translational open reading frame of the DG17 gene encoded a 458-amino-acid cysteine- and lysine-rich protein of unknown function. In several regions, the cysteine and lysine residues were arranged in a manner characteristic of the zinc-binding domains found in proteins which interact with nucleic acids. During normal development, the DG17 and CP1 genes are coordinately activated late in aggregation. The addition of exogenous cyclic AMP (cAMP) induced the premature expression of both mRNAs. By measuring the rate of specific mRNA synthesis in isolated nuclei, we showed that cAMP acted at the transcriptional level to activate both genes. The two genes were separated by 910 nucleotides and were divergently transcribed. The intergenic region was predominantly composed of A + T residues except for four short G-rich regions. These sequences coincided with the positions of four nuclease-hypersensitive sites, which appear during aggregation when the DG17 and CP1 genes are transcribed (J. Pavlovic, E. Banz, and R. W. Parish, Nucleic Acids Res. 14:8703-8722, 1986). Two of the G-rich regions formed the core of two almost identical 80-nucleotide repeats located 220 and 320 nucleotides upstream of the CP1 gene. Using the Dictyostelium transformation system, we showed that a restriction fragment containing the intergenic region was capable of directing bidirectional transcription in a cAMP-dependent manner.