Mapping of the ErbB3 interaction domain within RGS4. (A) RGS4-NubG
deletion constructs. RGS4 contains an N-terminal amphipathic region important
for membrane localization (amino acid 1–33, striped box) followed by the
RGS box (amino acid 58–178, grey box) and the C-terminal tail (amino
acid 179–205). The NubG domain of ubiquitin is shown as a dotted
ellipse. (B) Quantitative β-galactosidase assay showing the
binding of different RGS4-NubG deletion mutants to the ErbB3-Cub-TF bait.
Values given are the mean of four transformants, each assayed at least twice.
The asterisk indicates the original RGS4 clone isolated in the split-ubiquitin
membrane yeast two-hybrid screen. (C) Expression and localization of
the RGS4–2HA-NubG deletion mutants. The RGS4–2HA-NubG deletion
mutants were generated by PCR followed by in vivo recombination into the prey
plasmid pADH-PREY-2HA-NubG previously digested with NdeI. Western
blot analyses were performed using membrane (left panels) and
cytosolic (right panels) fractions of the yeast L40 reporter strain
expressing ErbB3-Cub-TF and the prey NubG (lane 1), RGS4-NubG
(1–178; lane 2), RGS4-NubG (1–205; lane 3),
RGS4-NubG (34–205; lane 4), RGS4-NubG (1–148; lane
5), RGS4-NubG (58–178; lane 6), and RGS4-NubG
(58–148; lane 7). The blots were incubated with anti-RGS4
antibody. The positions of molecular markers are indicated. The bands that are
not marked with an asterisk are considered as degradation products of RGS4.
The RGS4-NubG (1–178) protein found in the split-ubiquitin membrane
yeast two-hybrid screen (lane 2) migrates more slowly than the
RGS4-NubG (1–205; lane 3) because it contains an additional 45
amino acids upstream of the initial RGS4 start codon.