Construction of hygromycin-resistant retroviral cloning vectors.

We report the construction of pIIGBl and pIIGB2, two retroviral vectors which enable selection by use of hygromycin, a powerful inhibitor of mammalian cell growth, thus making it possible to coinfect cells with a retrovirus carrying a different selective marker or to infect cells already transfected with eucaryotic expression plasmids. Expression cloning in these vectors utilizes a TK promoter, which, in this construct, is active in every cell clone examined, a finding not frequently observed for promoters carried by other retroviral vectors (1). As cell manipulation by retroviral insertion is limited by the combination of promoters and cloning sites available, we believe that these constructs may be useful under several circumstances. For example, in conjuction with pXTl, a vector carrying neoR and the TK promoter (2), cDNAs encoding subunits for heterodimeric proteins such as MHC class II antigens or T-cell receptors can be introduced into the same cell. This work was supported by the Associazione Italiana per la Ricerca sul Cancro (AIRC).