Table 1.
Expression of β-gal by different SIN replicons
Replicon, noncytopathic/cytopathic | μg of β-gal/106 cells* |
---|---|
SINrep19/lacZ, noncytopathic | 1.4 ± 0.1 |
SINrep3/lacZ, cytopathic | 40 ± 2.4 |
SINrep18 + DI/lacZ-neo, noncytopathic | 31 ± 1.7 |
Amounts of β-gal were determined by comparison with concentration standards in enzymatic activity assays. Cell lysates were prepared following 2 days of puromycin selection (for noncytopathic replicons) or 18 h after infection at a moi of 10 (packaged cytopathic replicons). For the noncytopathic replicons, expression levels plateau after 2 days of selection; for the cytopathic replicons, 18 h precedes the onset of cytopathic effect although expression levels are only one-half maximal at this time. Standard BHK cells expressed undetectable β-gal activity. The sensitivity of this assay was ≈1 ng of purified enzyme. Values shown reflect the mean and SD for three replicate experiments.