Structure of Herpesvirus saimiri genomes: arrangement of heavy and light sequences in the M genome

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Abstract
Herpesvirus saimiri contains 2 species of DNA molecules. The M genome is composed of 70% light (L) DNA (36% cytosine plus guanine, density in CsCl 1.695 g/ml), which consists of unique sequences, and 30% heavy (H) DNA (71% cytosine plus guanine, density 1.729 g/ml). The H genome contains heavy sequences exclusively. H sequences in M and H genomes cross-hybridize completely and are cleaved identically by restriction endonuclease R.cntdot.Sma I [from Serratia marcescens] into 4 classes of fragments with MW of about 360,000, 300,000, 130,000 and 40,000, respectively. H sequences are chains of identical repeat units in tandem arrangement. The MW of each repeat unit is about 830,000. L sequences have no cleavage site for endo R.cntdot.Sma I. H sequences are terminally arranged at both ends of the M genome, as seen by EM after partial denaturation. The length of the individual heavy ends varies between 21 .mu.m and < 1 .mu.m, whereas the light region is uniform in size (35.3 .+-. 0.35 .mu.m). As a rule, molecules with a long heavy end at 1 side have a short heavy end at the other side, thus giving rise to a limited size heterogeneity. Orientation of M DNA molecules by the denaturation map of the light region shows that the longer heavy end may be located at the left or at the right side of the M genome.