In mouse hepatitis virus (MHV)-infected cells, newly synthesized RNA was detected in close proximity to DMVs and CMs, and viral RNA levels correlated with the number of DMVs. However, other data do not necessarily support the active contribution of DMVs to viral RNA synt hesized. Nascent MHV RNAs colocalize with dsRNA only at early times postinfection; at later times, the dsRNA distributed throughout the cell is apparently transcriptionally inactive. Furthermore, RdRp or nascent viral RNA has not been detected inside DMVs, and ultrastructural analysis could not confirm any connection  between the DMV interior and cytoplasm, raising questions about the import and export of ribonucleotide precursors and produced RNAs exported from RNA synthesis areas.