Ka. Sommer et al., THE GENE UPSTREAM OF DMRP128 CODES FOR A NOVEL GTP-BINDING PROTEIN OFDROSOPHILA-MELANOGASTER, MGG. Molecular & general genetics, 242(4), 1994, pp. 391-398
Upstream of the gene coding for the second-largest subunit of RNA poly
merase III (DmRP128) we have found another gene (128up), which is tran
scribed in the same direction as the RNA polymerase gene. The intergen
ic distance between the 3' end of 128up mRNA and the 5' end of DmRP128
mRNA is only about 100 bp. Transcripts of 128up are present at a much
higher level than DmRP128 RNA in Drosophila Schneider 2 cells, embryo
s, and adult flies. Two transcription start points, seven nucleotides
apart, are found for 128up compared to multiple scattered starts for D
mRP128. Sequence analysis of 128up cDNA reveals that the gene codes fo
r a 41 kDa protein with homology to GTP-binding proteins and matching
four of the structural sequence motifs characteristic of the superfami
ly of GTPases. Bacterially expressed 128up protein fused to maltose-bi
nding protein specifically binds GTP. Sequences closely related to the
128up protein are found in species as distant as Halobacterium, yeast
or mouse; the murine protein is 80% identical to 128up. This evolutio
nary conservation is indicative of an important, but as yet unknown, p
hysiological role. In accordance with the sequence conservation, antib
odies against 128up specifically cross-react with mouse 3T3 cells and
human Hep2 cells where the subcellular localization of the protein is
predominantly perinuclear. We propose that 128up is a member of a nove
l class of GTP-binding proteins.