A 15-kilobase-pair region of the human cytomegalovirus genome which includes US1 through US13 is dispensable for growth in cell culture.

The genome of a temperature-sensitive, DNA-negative mutant of human cytomegalovirus was cloned in cosmids and analyzed by restriction endonuclease mapping and Southern blotting. The data presented show that in the mutant genome, nearly half of the short segment was deleted (14.3 to 15.1 kb; map position, 0.83 to 0.9), including the genes for a potential immediate early protein (US3) and a structural glycoprotein of 47 to 52 kDa (US6 through US11). The deleted DNA region was replaced by a 20.8- to 21.6-kb fragment that represented an inverted repetition of the retained portion of the short segment (map position, 0.92 to 1.0), suggesting that US20 through US36 were duplicated in the mutant. Northern (RNA) blots with appropriate probes of total cell RNA extracted from mutant-infected cells confirmed the absence of mRNAs originating from US3 or from US8 through US11. It is concluded that the deleted genes are dispensable for human cytomegalovirus replication in cell culture.