THE REGULATOR OF EARLY GLIOGENESIS GLIAL-CELLS MISSING IS A TRANSCRIPTION FACTOR WITH A NOVEL TYPE OF DNA-BINDING DOMAIN

Absence or presence of glial cells missing (GCM) in cells of the devel oping nervous system of Drosophila decides over their future fate as n eurons or glia with only those cells turning into glia that express GC M. To understand how GCM exerts its function we performed a detailed s tructure-function analysis. Using fusions between the DNA binding doma in of the yeast GAL4 protein and GCM, we detected a transactivation fu nction within the C-terminal part of GCM, In addition to this transact ivation domain we mapped a sequence-specific DNA-binding domain within the N-terminal part of the GCM protein in close proximity to a bipart ite nuclear localization signal, Binding site selection assays determi ned the motif 5'-AT(G/A)CGGGT-3' as the preferred binding site for GCM , Both the lack of homology to known proteins and the novel DNA bindin g specificity indicate that GCM contained a new type of DNA-binding do main, In transiently transfected cells, GCM also activated transcripti on from promoters consisting of the newly identified GCM-binding site and a TATA box, Thus, GCM is a novel type of transcription factor invo lved in early gliogenesis.