EFFECT OF EXPRESSION OF THE APHTHOVIRUS PROTEASE 3C ON VIRAL-INFECTION AND GENE-EXPRESSION

Cells transformed with specific regions of the foot-and-mouth disease virus (FM DV) genome have been constructed and analyzed with respect t o viability and susceptibility to FMDV infection. Constitutive express ion of an active protease 3C under the control of the tk promoter has been documented by the ability of transformed cells to catalyze the pr ocessing of a P1 capsid precursor. High-level, transient expression bu t not low-level, constitutive expression, of 3C caused a 10-fold reduc tion in the yield of FMDV and was detrimental to the expression of the cotransfected reporter luciferase gene. No such effect was observed i n assays involving cells transfected with a deleted, inactive form of 3C. The negative effect of 3C was not observed when the same reporter gene was integrated and expressed in a constitutive fashion nor when i ts translation was directed by the internal ribosome entry site elemen t of FMDV in transient expression assays. The results show that cells with a low level of expression of the aphthoviral 3C can be stably mai ntained and can provide a useful tool to study polyprotein processing. (C) 1995 Academic Press, Inc.