The P30 movement protein (MP) of tobacco mosaic virus is essential for dist
ribution of sites of replication within infected cells and for cell-cell sp
read of infection. MP is an integral membrane protein and in early and mid-
stages of infection causes severe disruption of the cortical endoplasmic re
ticulum (ER). MP also associates with microtubules, and in late stages is t
argeted for degradation by the 26S proteosome. During these stages, the ER
regains its normal pre-infection configuration. Viral RNA is associated wit
h ER and microtubules in the presence of MP. The MP is phosphorylated and m
utation of the phosphorylated amino acid reduced association of MP with the
ER, plasmodesmata, and microtubules, and altered the stability of the MP.
The nature of the association of MP with vRNA and ER and microtubules, and
the role of phosphorylation of MP in each of these functions, if any, remai
ns to be determined.