SAX and MAX 
A 0.7 kb (KpnI-Bglll ) DNA fragment encoding the mouse 
metallothionein I promoter (MT) and a 0.4 kb DNA fragment (KpnI-Hindlll ) 
encoding the early SV40 promoter were fused to the 1300 bp human ADA cDNA 
(EcoRX-AccI) and inserted into the Xhol site of the N2 vector in the same 
transcriptional orientation as the viral transcriptional unit. Virus was 
generated by transfection of the vector DNA into til cells and infection of PA12 
cells (11,12). The titer of virus was determined as infectious Neo containing 
viruses per ml of supernatant. The two to four-fold variations in virus titer 
represents the variations in measured titer among 3-5 independently derived high 
titer producer cell lines. 
Recombinant DNA Research, Volume 12 
[ 261 ] 
