INHIBITION OF VACCINIA VIRUS-REPLICATION BY N-(PHOSPHONOACETYL)-L-ASPARTATE - DIFFERENTIAL-EFFECTS ON VIRAL GENE-EXPRESSION RESULT FROM A REDUCED PYRIMIDINE NUCLEOTIDE POOL

The replication of vaccinia virus was reduced by 3 logs in cells that had been treated before and during infection with a concentration of N -(phosphonoacetyl)-L-aspartate (PALA) which lowered the UTP and CTP to 5 and 20% of controls, respectively, without affecting cell viability . The antiviral activity of PALA was reversed with uridine, indicating that it was entirely due to the diminution in pyrimidine nucleotides. Analysis of Viral proteins revealed prolonged synthesis of some early stage species but a drastic reduction in late stage species, even tho ugh the nucleotide concentrations remained relatively constant through out the infection. Although the gene expression pattern resembled that caused by a potent inhibitor of DNA synthesis, viral DNA accumulation was reduced by only 60%. Very little of the DNA made in the presence of PALA was converted to genome length molecules. The effect of PALA o n transcription of early genes was complex: there was a twofold increa se in the amount of a relatively short mRNA of 500 nucleotides but a t wo-to threefold decrease in the amount of a 4300-nucleotide mRNA encod ing the largest subunit of RNA polymerase. In contrast, PALA severely inhibited the accumulation of viral intermediate and late stage mRNAs. The extreme sensitivity of vaccinia virus to PALA and the differentia l effects of the drug on viral gene expression result from the cascade mechanism of viral gene regulation. (C) 1997 Academic Press.