in 293T and will transiently maintain a high copy number; this can greatly increase the amount of recombinant protein or retrovirus that can be produced from the cells. The full genome sequences of three different isolates of 293T have been determined. They are quite similar to each other but show detectable divergence from the parental HEK 293 cell line. Applications HEK 293 cells are straightforward to grow in culture and to transfect. They have been used as hosts for gene expression. Typically, these experiments involve transfecting in a gene (or combination of genes) of interest, and then analyzing the expressed protein. The widespread use of this cell line is due to its transfectability by the various techniques, including calcium phosphate method, achieving efficiencies approaching 100%. Examples of such experiments include: Effects of a drug on sodium channels Inducible RNA interference system Isoform-selective protein kinase C agonist Interaction between two proteins Nuclear export signal in a protein HEK 293 cells were adapted to grow in suspension culture, as opposed to proliferation on plastic plates, in 1985. This enabled the growth of large amounts of recombinant adenovirus vectors. A more specific use of HEK 293 cells is in the propagation of adenoviral vectors. Viruses offer an efficient means of delivering genes into cells, which they evolved to do, and are thus of great use as experimental tools. However, as pathogens, they also present a risk to the experimenter. This danger can be avoided by the use of viruses which lack key genes, and which are thus unable to replicate after entering a cell. In order to propagate such viral vectors, a cell line that expresses the missing genes is required. Since HEK 293 cells express a number of adenoviral genes, they can be used to propagate adenoviral vectors in which these genes (typically, E1 and E3) are deleted, such as AdEasy. However, homologous recombination between the inserted cellular Ad5 sequence and the vector sequence, although rare, can restore the replication capacity to the vector. An important variant of this cell line is the 293T cell line. It contains the SV40 large T-antigen that allows for episomal replication of transfected plasmids containing the SV40 origin of replication. This allows for amplification of transfected plasmids and extended temporal expression of desired gene products. HEK 293, and especially HEK 293T, cells are commonly used for the production of various retroviral vectors. Various retroviral packaging cell