Intracellular type A retrovirus movement associated with an intact microtubule system

Intracytoplasmic type A particles known to be precursors to type B retroviruses in murine, hamster and marsupial cells are closely associated with microtubules and microtubule organizing centres. In this publication, the active participation of microtubules in the intracellular transport of the particles to the cell surface has been examined in NIH 3T3 cells infected with M432 virus using vincristine sulphate (VCR) as inhibitor of microtubule polymerization. The release of virus at different times after exposure to VCR was quantified by reverse transcriptase determinations of cell supernatants and by electron microscopic quantification of the number of virions at the cell surface using freeze-dried whole cell replicas. These studies indicate that VCR inhibits both microtubule polymerization and virus release, and thus suggest that intact cytoplasmic microtubules are necessary for intracellular transport and release of virus.