Sequence comparisons of DmNopp140-RGG and
DmNopp140. (A) Acidic (black boxes) and basic (white boxes) regions
alternate within the central domains of both Drosophila
variants. This alternating pattern is similar to that within rat
Nopp140. DmNopp140 is the Drosophila homolog of
mammalian Nopp140, whereas DmNopp140-RGG is unique due to its
carboxyl-terminal RGG domain. (B) Expressed sequence tags exist for
both Drosophila variants. Restriction maps allowed us to
predict digestion patterns and thus to verify the clones. The purified
cDNA insert that encodes conceptual transcript 22833 (DmNopp140) was
left undigested (lane 1), incubated with PvuI that
failed to cut as predicted (lane 2), or digested with
AvaI that generated two bands of predicted size (lane
3). The purified cDNA insert that encodes conceptual transcript 22845
(DmNopp140-RGG) was left undigested (lane 4), incubated with
PvuI that generated two predicted fragments (lane 5), or
incubated with AvaI that failed to cut as expected (lane
6). The digestion patterns confirmed the existence of two separate cDNA
clones. (C) The deduced amino acid sequence of DmNopp140-RGG. CT22845
consists of three exons. The first encodes amino acids 1–34, the
second encodes 35–551, and the third encodes 552–688. The serine-rich
acidic regions are highlighted in light gray. MPF phosphorylation
motifs are in bold. The RGG domain spans residues 612–669. Two
additional upstream RGG motifs reside at 562–567. (D) The deduced
amino acid sequence of DmNopp140. CT22833 consists of four exons. The
first two exons are identical to those in CT22845. Thus, the two
proteins are identical up to residue 551 (dark gray box), after which
their sequences diverge. The third exon in CT22833 encodes residues
552–604 and the fourth exon encodes residues 605–654. The carboxy
terminus of DmNopp140 is 64% identical to the carboxy terminus of rat
Nopp140. A highly conserved serine residue within this terminus
(residue 610 in the black box) is a putative substrate site for
cAMP-dependent protein kinase.