Phage lambda DNA injection into Escherichia coli pel- mutants is restored by mutations in phage genes V or H.

Mouse cells in culture contain two distinct forms of thymidine kinase enzyme activities. These two enzymes have been separated by polyacrylamide gel electrophoresis into a 0.2 R_f and a 0.5 R_f activity. The 0.2 R_f enzyme was found only in actively growing cells, while the 0.5 R_f form of thymidine kinase is the mitochondrial-associated enzyme and is most prominent in resting cells in culture. SV40 infection of these resting cells results in an increased specific activity of only the 0.2 R_f form of this enzyme.SV40 wild-type and SV40 tsBC and tsC mutants stimulated the levels of the 0.2 R_f thymidine kinase in resting cells after viral infection at either the permissive temperature (32°) or the nonpermissive temperature (41°). Five different SV40 tsA mutants (tsA7, 28, 30, 58, and 209) and two different SV40 tsD mutants (tsD202, 270) only stimulated thymidine kinase activity at the permissive temperature. Little or no 0.2 R_f thymidine kinase activity could be detected in tsA or tsD mutant-infected cells at the nonpermissive temperature. The SV40 tsA255 mutant appeared to be an exception to the A mutant class in that it stimulated the 0.2 R_f thymidine kinase activity at both permissive and nonpermissive temperatures.These results indicate that the SV40 A gene product may be required directly, and the D gene product indirectly, in the stimulation of cellular enzyme activities following viral infection.