“…For cloning of point mutations 520H Q (strain CMV-6, a kind gift from A. Erice, University of Minnesota Medical School, MS, USA) (Hanson et al, 1995) and 594A V (Chou et al, 1995) (done in the laboratory of G. Gerna, Servizio di Virologia, Pavia, Italy) in the UL97 ORF of GCV-resistant clinical isolates, the previously described primers pri.5-KpnI and pri.6-EcoRI (Metzger et al, 1994) were used for amplification of an appropriate fragment of DNA from the clinical isolates. The mutation at amino acid position 460M (Lurain et al, 1994) was introduced by site-directed mutagenesis according to the method of Landt et al (1990) by using the mutated primer 5h ATT ACA CCC GTG AAC GTG C 3h for amplification.…”