Identification of cis-Regulating Elements andtrans-Acting Factors Regulating the Expression of the Gene Encoding the Small Subunit of Ribonucleotide Reductase inDictyostelium discoideum

Abstract

We have examined the promoter of rnrB, the gene encoding the small subunit of ribonucleotide reductase of Dictyostelium discoideum, using lacZ as a reporter gene. Deletion analysis showed that expression of this gene in vegetative cells involves an A/T-rich element, whereas its expression in prespore cells during development requires a region encompassing two G/C-rich elements, designated box A and box B. Removal of boxes A and B results in very low level of activity. When either box A or box B is deleted, prestalk cells adjacent to the prespore zone also express ␤-galactosidase. The behavior of these cis-regulatory elements implies that the mechanism regulating the prespore-specific expression of rnrB is different from that regulating other known prespore genes.We have used electrophoretic mobility shift assays to identify factors that interact with box A and box B. Box A interacts with a factor that is found in the nuclear fraction. While box B interacts with a factor that is present in the cytosolic fraction throughout growth and development, its presence in the nuclear fraction is developmentally regulated. Results from competition assays suggest that both box A and box B interact with transcriptional activators that have not been characterized previously.

Biphasic expression of rnrB in Dictyostelium discoideum suggests a direct relationship between cell cycle control and cell differentiation

“…The reporter construct employs a 450 bp promoter which appears to contain all elements necessary for cell cycle regulation; thus it does not appear that either of the introns [95] is required. The 450 bp promoter contains 4 GC‐rich elements which are necessary for the expression of rnrB in developing Dictyostelium cells, as well as an AT‐rich element which appears sufficient for expression in vegetative growth [17]. We do not yet know which of these elements is important for cell‐cycle regulated transcription in Dictyostelium .…”

Prespore cell inducing factor, ψ factor, controls both prestalk and prespore gene expression in Dictyostelium development

“…3A). The promoter regulating rnrB expression was analysed previously (Bonfils et al. 1999) and it was shown that expression of rnrB during the multicellular stage is induced by a cell type non‐specific activator, which is repressed in prestalk cells via a G/C rich element.…”

“…However, the failure of prestalk repression occurred in different situations for rnrB and cudA ; the former was revealed when psiA was knocked out, while ectopic expression was seen in the latter when psiA was overexpressed. The promoters of both genes have been analysed extensively, and, as for rnrB, the minimal promoter construct Δ‐280, which contains only a boxA alone, is sufficient to confer prespore specific expression in wild type slugs (Bonfils et al. 1999).…”

Molecular analysis and functions of p53R2 in zebrafish

“…It has been shown that expression of mammalian and other RNR small subunits can be induced by various kinds of DNA damage (Elledge et al, 1993;Bonfils et al, 1999;Tanaka et al, 2000;Kimura et al, 2003;Jayachandran and Fallon, 2004). The induction of mammal p53R2 by DNA damage is closely associated with p53 activity (Tanaka et al, 2000;Kimura et al, 2003).…”