Caulimoviruses: Molecular Biology

Caulimoviruses constitute the best studied of six genera of the family Caulimoviridae or plant pararetroviruses. They have icosahedral capsids harbouring ?8000bp long double stranded open circular DNA. In infected nuclei their genome exists also in form of circular minichromosomes, from which terminally redundant RNA is produced. This is packaged into the capsids and reverse transcribed, a process related to the genome replication of animal retroviruses. The pregenomic RNA serves also as polycistronic mRNA with seven open reading frames, which are translated by an unusual reinitiation mechanism directed by one of its geneproducts, the polyfunctional transactivator of translation/viroplasmin (TAV). Furthermore cauimovirus RNAs have a characteristic highly structured leader region, which is bypassed by the scanning ribosomes by a shunting mechanism. Mature virions accumulate in inclusion bodies formed by TAV, are transported through movement protein channels from cell to cell and transmitted by aphids.