In work appearing in this week's edition of PNAS, Tel Aviv University's Ronen Borenstein and Niza Frenkel describe single-step production of viral BACs of the 160-kb human herpes virus 6A. Their method of cloning, they say, is "independent of intracellular recombinations and DNA packaging constraints" and is "especially attractive for viruses that replicate inefficiently and for viruses propagated in suspension cells."