CHARACTERIZATION OF THE SIGNAL-TRANSDUCTION PATHWAYS AND CIS-ACTING DNA-SEQUENCE RESPONSIBLE FOR THE TRANSCRIPTIONAL INDUCTION DURING GROWTH AND DEVELOPMENT OF THE LYSOSOMAL ALPHA-MANNOSIDASE GENE IN DICTYOSTELIUM-DISCOIDEUM
J. Schatzle et al., CHARACTERIZATION OF THE SIGNAL-TRANSDUCTION PATHWAYS AND CIS-ACTING DNA-SEQUENCE RESPONSIBLE FOR THE TRANSCRIPTIONAL INDUCTION DURING GROWTH AND DEVELOPMENT OF THE LYSOSOMAL ALPHA-MANNOSIDASE GENE IN DICTYOSTELIUM-DISCOIDEUM, The Journal of biological chemistry, 268(26), 1993, pp. 19632-19639
The lysosomal alpha-mannosidase gene in Dictyostelium discoideum is re
presentative of a small group of genes that are expressed under two di
fferent 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 alp
ha-mannosidase gene induced by starvation did not require protein synt
hesis in axenic wild-type strains, whereas protein synthesis was requi
red for the transcriptional induction observed in response to PSF. Nor
thern blot analysis was also done using mRNA from Galpha1 and Galpha2
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 se
creted glycoprotein conditioned medium factor or the cAMP receptor-1 p
rotein. 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 requir
ed for alpha-mannosidase transcriptional induction under both starvati
on conditions and in response to PSF. The TTG box identified is an imp
ortant regulatory element in the promoter of another prestarvation res
ponse gene, the discoidin Igamma gene. A ts mutant was found to misreg
ulate the expression of both discoidin I and alpha-mannosidase express
ion at restrictive temperatures. Taken together these results suggest
that the prestarvation response genes may be coordinately regulated po
ssibly through the TTG box.