Accessory functions capable of supporting efficient recombinant AAV (rAAV)
virion production in a suitable host cell are provided. The accessory
functions are in the form of one or more vectors that are capable of
being transferred between cells. Methods of producing rAAV virions are
also provided. The methods can be practiced to produce commercially
significant levels of rAAV particles without also generating significant
levels of infectious helper virus or other contaminating by-products.