- Volume 40, Issue 3, 1978

The association of newly synthesized vaccinia virus DNA with proteins in infected HeLa cells was followed. A shift from a high density to a low density complex occurred between 3 and 6 h after infection. This process was not affected by isatin β thiosemicarbazone (IBT), an inhibitor of pox virus growth. At 22 h after infection in the absence of IBT, mature virions of high density were observed; however, in the presence of the drug, high density DNA-protein complexes, which lack the two main virus core polypeptides, were formed.

Rous sarcoma virus (RSV) mutants, which bear temperature sensitive (ts) defects in both the maintenance of cell transformation and the expression of tumour specific cell surface antigen(s) (TSSA), have yielded a number of revertants. In seven revertants studied, the acquisition of wild type transforming capacities is always accompanied by a wild type TSSA expression. This strongly indicates that transformation and TSSA expression in RSV are affected by the same mutation.

An attempt was made to isolate a bacteriophage T4 mutant generally disturbed in its ability to exclude the localized exclusion sensitivity determinants of T2 from the progeny of crosses. The method used was a modification of that used previously, which revealed T4 mutants unable to exclude more than one of the T2 sensitive sites specifically. One out of 1000 isolates from a mutagenized T4 am56:am32 stock was found to be mutated in its exclusion properties. However, the mutant was not generally exclusion deficient. Its properties were similar to those of a double mutant T4 ex56:ex32, specifically unable to exclude the T2 sensitive sites near gene 56 and gene 32. The failure to isolate a generally excluding mutant at a frequency down to 10−3 renders the occurrence of a general exclusion locus unlikely.

The infectivity of RNA obtained from particles of tobacco ringspot and tomato black ring viruses by treatment with phenol was inactivated on incubation with proteinase K or Pronase, whereas the infectivity of tobacco rattle virus RNA was not affected. The size distribution of molecules of tobacco ringspot virus RNA, assessed by polyacrylamide gel electrophoresis, was not altered by the protease treatments. Infectivity was abolished by treating either RNA-1 or RNA-2 of tomato black ring virus with proteinase K, indicating that a protease-sensitive structure needed for infectivity is attached to each RNA species. The properties of this structure are compared to those of the proteins that are covalently bonded to the genome nucleic acids of some vertebrate and bacterial viruses.