In vivo replication of recombinant murine cytomegalovirus driven by the paralogous major immediate-early promoter-enhancer of human cytomegalovirus

Transcription of the major immediate-early (MIE) genes of cytomegaloviruses (CMV) is driven by a strong promoter-enhancer (MIEPE) complex. Transactiva tor proteins encoded by these MIE genes are essential for productive infect ion. Accordingly, the MIEPE is a crucial control point, and its regulation by activators and repressors is pertinent to virus replication. Since the M IEPE contains multiple regulatory elements, it was reasonable to assume tha t specific sequence motifs are irreplaceable for specifying the cell-type t ropism and replication pattern. Recent work on murine CMV infectivity (A. A ngulo, M. Messerle, U. H. Koszinowski, and P. Ghazal, J. Virol. 72:8502-850 9, 1998) has documented the proposed enhancing function of the enhancer in that its resection or its replacement by a nonregulatory stuffer sequence r esulted in a significant reduction of infectivity, even though replication competence was maintained by a basal activity of the spared authentic MIE p romoter. Notably, full capacity for productive in vitro infection of fibrob lasts was restored in recombinant viruses by the human CMV enhancer. Using two-color in situ hybridization with MIEPE-specific polynucleotide probes, we demonstrated that a murine CMV recombinant in which the complete murine CMV MIEPE is replaced by the paralogous human CMV core promoter and enhance r (recombinant virus mCMVhMIEPE) retained the potential to replicate in viv o in all tissues relevant to CMV disease. Notably, mCMVhMIEPE was also foun d to replicate in the liver, a site at which transgenic hCMV MIEPE is silen ced. We conclude that productive in vivo infection with murine CMV does not strictly depend on a MIEPE type-specific regulation.