TKT and infection: Taken together with our results and those for ORF21/TK orthologs of the gammaherpesvirus, KSHV ORF21 is thought to contribute to the new infection through three mechanisms: (i) enhancement of infectivity of progeny virus, (ii) establishment of novel infection in the host cell after invasion into the cell, and (iii) the spread of the virus by promoting the migration of infected cells.