Cl. Thomas et Aj. Maule, IDENTIFICATION OF STRUCTURAL DOMAINS WITHIN THE CAULIFLOWER MOSAIC-VIRUS MOVEMENT PROTEIN BY SCANNING DELETION MUTAGENESIS AND EPITOPE TAGGING, The Plant cell, 7(5), 1995, pp. 561-572
Plant viruses encode proteins that mediate their movement from cell to
cell through plasmodesmata. Currently, the mechanisms of action of th
ese movement proteins (MPs) can be divided broadly into two types, req
uiring or not requiring the presence of viral capsid protein. Cauliflo
wer mosaic virus encodes a multifunctional MP (P1) that modifies plasm
odesmata through the formation of tubules that contain virus particles
. To investigate the structure of P1, 26 small deletions (scanning del
etions) were used to characterize regions of P1 essential for full bio
logical activity. These deletions identified an N-terminal region and
a region close to but not at the C terminus as domains that could tole
rate manipulation, although gross deletions of either domain abolished
infection. In sequence comparisons with other caulimovirus MPs, these
regions coincided with the areas of least amino acid homology. Epitop
e tags inserted into either of these regions were stably maintained in
systemic infections, and in extracts from infected plants, tagged P1
was detected on immunoblots. We predicted that, from the hypervariabil
ity of these regions, they would be located on the surface of the nati
ve P1 structure. Immunofluorescence of P1-specific tubules formed on t
he surface of infected protoplasts confirmed that the N-terminal and C
terminus-proximal regions were exposed-on the surface of the P1 tubul
e subunit. These findings establish a structure for P1 that is likely
to be applicable to other tubule-forming MPs.