Each flashBAC™ selection box contains either a single 3 reaction kit of flashBAC™, flashBAC™ GOLD and flashBAC™ ULTRA (Box 1) or a single 3 reaction kit of  flashBAC™, flashBAC™ GOLD, flashBAC™ ULTRA and flashBAC™ PRIME (Box 2). The original flashBAC™ expression vector is a good choice for projects where the gene to be expressed is likely to be simple and expressed in the cytoplasm or nucleus. flashBAC™ GOLD is enhanced by the deletion of the chiA (chitinase) and v-cath (cathepsin) protease genes. It provides superior levels of expression for any protein that is destined for secretion or to be inserted in the membrane, or for any protein that might be particularly liable to degradation. flashBAC™ ULTRA contains deletions of the chitinase and cathepsin genes, as above, but also deletions of the p10, p74 and p26 genes and provides the best choice for the most difficult to express proteins; suitable for cytoplasmic, nucleus, secreted and membrane proteins. flashBAC™ PRIME contains no gene deletions and has proven useful for the release and subsequent purification of intracellular VLPs and protein complexes