Organization and expression of calicivirus genes

The application of molecular techniques to the characterization of calicivi ruses has resulted in an extensive database of sequence information. This i nformation has led to the identification of 4 distinct genera, The human en teric caliciviruses have been assigned to 2 of these genera, This division is reflected not only in sequence diversity but in a fundamental difference in genome organization. Complete genome sequences are now available for 5 enteric caliciviruses and demonstrate that human and animal enteric caliciv iruses are phylogenetically closely related. Currently, there is no cell cu lture system for the human viruses; therefore, studies have relied on heter ologous expression and in vitro systems. These studies have shown that in b oth human and animal viruses the viral nonstructural proteins are produced from a polyprotein precursor that is cleaved by a single viral protease. Th e purpose of this article is to provide an overview of the current knowledg e of genome structure and gene expression in the enteric caliciviruses.