The amino-terminal domain of the large subunit of herpes simplex virus type 2 (HSV-2) ribonucleotide reductase (ICP10) has protein kinase (PK) activity and properties similar to those of growth factor receptor kinases which can be activated to transforming potential. DNA sequences that encode the PK domain cause neoplastic transformation of immortalized cells. The studies described in this report used a spontaneous mutant (5-152) temperature-sensitive for the synthesis of ICP10 and the previously described ICP10 expression vectors to study the role of ICP10 expression in HSV-2 growth and neoplastic potential. The titres of the 5-152 mutant are 1000-fold lower at 39 °C compared to 34 °C after 12 h post-infection. The efficiency of plaquing is 0.003. The growth defect at 39 °C correlates with decreased ICP10 synthesis. Sequence analysis of the PK domain of the 5-152 ICP10 gene identified a pair of frameshift mutations resulting in a 19 amino acid residue substitution at positions 275 to 293 and a downstream single base pair mutation causing a substitution at position 309. Cloning of the mutant ICP10 gene from 5-152 into a wild-type HSV-2 isolate resulted in a recombinant (859/152) with growth properties and rates of ICP10 synthesis at 39 °C similar to those of 5-152. Cells transformed with u.v.-inactivated 5-152, or the recombinant 859/152, have significantly decreased cloning efficiency in agarose at 39 °C, but only during the first 250 post-transfer population doublings. Anchorage-independent growth was observed in cells transfected with expression vectors pJW17 or pJW32 that express ICP10 or its PK domain, respectively. Cells transfected with the frameshift mutant pJW21 or the ICP10 carboxy-terminal vector pJW31 did not form clones in agarose.


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