Isolation and preliminary characterization of temperature-sensitive mutants of human cytomegalovirus

Thirteen temperature-sensitive (ts) mutants of human cytomegalovirus (HCMV) have been isolated after mutagenesis with nitrosoguanidine or ultraviolet light. Four mutants defective in viral DNA synthesis at nonpermissive temperature (DNA-) were classified into two separate complementation groups. The other nine HCMV ts mutants, capable of synthesizing viral DNA at the elevated temperature (DNA+), belonged to seven independent complementation groups. The number of essential genes encoded by HCMV is thus raised here by nine.