Mutation of glutamine to arginine at position 548 of IE2 86 in human cytomegalovirus leads to decreased expression of IE2 40, IE2 60, UL83, and UL84 and increased transcription of US8-9 and US29-32.

The IE2 86 protein of human cytomegalovirus (HCMV) is essential for productive infection. The mutation of glutamine to arginine at position 548 of IE2 86 causes the virus to grow both slowly and to very low titers, making it difficult to study this mutant via infection. In this study, Q548R IE2 86 HCMV was produced on the complementing cell line 86F/40HA, which allowed faster and higher-titer production of mutant virus. The main defects observed in this mutant were greatly decreased expression of IE2 40, IE2 60, UL83, and UL84. Genome replication and the induction of cell cycle arrest were found to proceed at or near wild-type levels, and there was no defect in transitioning to early or late protein expression. Q548R IE2 86 was still able to interact with UL84. Furthermore, Q548R IE2 40 maintained the ability to enhance UL84 expression in a cotransfection assay. Microarray analysis of Q548R IE2 HCMV revealed that the US8, US9, and US29-32 transcripts were all significantly upregulated. These results further confirm the importance of IE2 in UL83 and UL84 expression as well as pointing to several previously unknown regions of the HCMV genome that may be regulated by IE2.