Nature of the block in the expression of some early virus genes in cells abortively infected with human cytomegalovirus.

Certain functions normally expressed during the early phase of productive human cytomegalovirus (HCMV) infection in human embryonic lung (HEL) cells are not expressed in abortively infected rabbit kidney (RK) cells. To determine the stage at which infection is blocked in RK cells, HCMV transcripts synthesized by these abortively infected cultures were compared to those synthesized during early stages of infection in productively infected HEL cells. The rate of accumulation of HCMV-specific RNA was approximately six- to eightfold lower in RK than in HEL cells during the first 24 hr postinfection. Although the rate of RNA accumulation did not decrease thereafter in RK cells, it did increase significantly in HEL cells and was dependent on the replication of virus DNA. Transcripts obtained from HEL cells 24 hr postinfection (either in the absence or presence of phosphonoacetic acid) and from abortively infected RK cells were analyzed by the Southern technique. Most of the "early" transcripts which accumulated in infected permissive cells were also present in the infected nonpermissive cells at 24 hr postinfection. However, some of the early transcripts (complementary to approximately 7% of the genome) were significantly underrepresented in RK cells. Furthermore, transcripts originating from one region of the genome, which were abundantly represented as cytoplasmic RNA both in productively and nonproductively infected cells, and which were polysome-associated in HEL cells, were found associated with polysomes in RK cells in very low amounts only. Northern blot analysis of the total and polysomal RNA from infected HEL cells and RK cells confirmed these findings. These results show that differences between productively infected HEL and nonproductively infected RK cells exist at the level of accumulation of some early transcripts, as well as at the level of association of some of these transcripts with polysomes.