TABLE 1.

Specific infectivity of RV M33 full-length cDNA clone

RNA used for transfection	Specific infectivity (plaques/μg)a
pBRM33 transcripts
No cap	0
m7G(5′)ppp(5′)G	3 × 103
pBRM34 transcriptsb
m7G(5′)ppp(5′)G	1.5 × 103
M33 RNA	2 × 104

^aVero cells were transfected with RNA transcripts and Lipofectin. After transfection, the cells were overlaid with agarose medium and incubated at 35°C for 6 days. The plaques were visualized by neutral red stain, and the specific infectivity of the RNA was determined from the number of plaques formed per microgram of RNA. 

^bpBRM34 is a restriction site variant of pBRM33 in which a new SphI site in the E1 transmembrane domain was created by changing T to A at nt 9647 in the pBRM33 clone.