Human cytomegalovirus DNA: restriction enzyme cleavage maps and map locations for immediate-early, early, and late RNAs

Complete physical maps for human cytomegalovirus (Davis strain) DNA were constructed from fragments produced by restriction endonucleases HindIII, XbaI, and EcoRI. The results showed that the human cytomegalovirus genome has a structural organization similar to that of the herpes simplex virus genome: a long (L) segment, comprising 82% of the genome, joined to a short (S) segment, comprising the remaining 18% of the genome. Permutations of the S and L segments produce four different molecular arrangements which are represented in equimolar proportions in virion DNA preparations. Heterogeneity in the size of the DNA was detected within fragments which map at one terminus of the S segment and also in fragments which map at one terminus of the L segment. The regions of the genome from which RNA synthesized at various times after infection originates was determined. Immediate-early RNA (RNA synthesized in the presence of cycloheximide) was restricted to a few regions on the genome but hybridized in abundance to a region which mapped between 0.686 and 0.733 units (within the L segment). Early RNA (synthesized in the absence of viral DNA synthesis) hybridized to most areas of the genome, but in particular abundance to a small region which mapped between 0 and 0.046 units (also within the L segment). RNA which accumulated during the late phase of infection was not characterized by particular abundances to any region of the genome.