Abstract: A method of packaging or encapsidating genetic material for use in gene transfer or cloning. An organism having a function or capability desired to be transferred or cloned is first selected. The DNA of this organism is extracted is cleaved to separate the exogenous genes controlling the function desired to be transferred or cloned. This exogenous gene is inserted in the linear DNA of a virus whose linear DNA has protein 5' termini, the virus DNA being extracted and cleaved so as to retain the genes specifying DNA replication. The resulting hybrid DNA is introduced into a cell-free in vitro medium along with a source of virus proheads and accessory viral structural and packaging proteins to assemble a hybrid virus encapsidating the hybrid DNA. This hybrid virus is similar in infectivity to the original or wild-type virus except that now either a segment of its DNA has been replaced by the desired exogeneous genes or the desired exogenous genes have been added to the viral DNA.