“…Nevertheless amplification of eDNA by the PCR may be worthy of investigation as a method of generating virus mutants. The finding that infectivity was reduced by addition of one G residue, and to a greater extent by two G residues, to the 5' end of the transcripts (Table 1) confirms the importance of the Y-terminal structure of transcripts for infectivity (Dawson et al, 1986;Van der Werf et al, 1987;Janda et al, 1987;Rice et al, 1987;Shaklee et al, 1988;Eggen et al, 1989a;Heaton et al, 1989) but, in contrast, infectivity appears to be relatively insensitive to T-terminal extensions (Janda et al, 1987;Eggen et al, 1989b). BamHI-cleaved pCMVI-(A to E), pCMV2-(A to E) and pCMV3-(A to E) contained four additional nucleotides beyond the 3' terminus of the RNAs; however, there was little difference between the infectivity of the transcripts and that of CMV-Q RNA.…”