The
lysosomal alpha-mannosidase gene in Dictyostelium discoideum is representative of a small group of genes that are expressed under two different conditions: 1) immediately upon removal of the bacterial food source from exponentially growing cells at < 5 x 10(5) cells/ml (which also initiates the developmental cycle), and 2) when the concentration of a secreted
glycoprotein termed the prestarvation response factor (PSF) reaches a critical threshold in cultures growing at densities > 5 x 10(5) cells/ml. In this report we show that transcription of the
alpha-mannosidase gene induced by
starvation did not require
protein synthesis in axenic wild-type strains, whereas
protein synthesis was required for the transcriptional induction observed in response to PSF. Northern blot analysis was also done using
mRNA from G alpha 1 and G alpha 2 gene disruption mutants. These genes encode subunits of
heterotrimeric G proteins found at the cell surface in growing cells and cells early in development. The pattern of
alpha-mannosidase gene expression was normal in these mutants as well as in mutants unable to produce the secreted
glycoprotein conditioned medium factor or the
cAMP receptor-1
protein. These genes have been shown to regulate the expression of many genes during early development. Promoter analysis studies identified
a 145-base pair sequence
element containing a TTG box which was required for
alpha-mannosidase transcriptional induction under both
starvation conditions and in response to PSF. The TTG box identified is an important regulatory
element in the promoter of another prestarvation response gene, the
discoidin I gamma gene. A ts mutant was found to misregulate the expression of both
discoidin I and
alpha-mannosidase expression at restrictive temperatures. Taken together these results suggest that the prestarvation response genes may be coordinately regulated possibly through the TTG box.