Light sensitive halogenated isomers (FU, BUDR) replace thymidine affects form but not function of viral progeny. Enzyme cutoff is inhibited. Puromycin remediates this.
Abstract
When rabbit kidney cells infected with pseudorabies virus are incubated with 5-
fluorouracil (FU) and 5-bromodeoxyuridine (BUDR), approximately 80% of the thymidine
in the progeny viral DNA is replaced by BUDR. These conditions do not
affect the initial increase of enzymatic activity and of DNA synthesis in the infected
cells. However, the drug prevents the normal cutoff of enzyme synthesis which occurs
by 6 hours after infection. BUDR also delays the loss of enzymatic activity that
takes place between 10 and 14 hours after infection.
The loss of enzyme activity, which occurs during the late stages of the infective
process, seems to result from the leakage of cellular constituents, including enzymes,
from the cells. Specific proteins, which are synthesized by the infected cells between
4 and 7 hours after infection, are responsible for this leakage. BUDR interferes with
the formation, not with the function, of these proteins.
The results of the experiments presented are consistent with the idea that incorporation
of BUDR into progeny viral DNA interferes with some of the aspects of the
infective process controlled by this DNA.
"That leakage from the cell is not correlated
with the formation within the cells of infectious
virus or viral coat proteins is concluded
from the following facts: (1) The addition of
puromycin to infected cells at any stage of
the infective process inhibits, as expected,
the subsequent formation of infectious virus;
the antibiotic, however, affects leakage from
the cells only when added during the early
stages of the infective process. (2) The proteins
responsible for leakage first appear at
approximately 4 hours after infection; viral
coat proteins, on the other hand, start being
synthesized at 2.5 hours after infection
(Hamada and Kaplan, 1965). (3) Leakage
is retarded in BUDR-treated infected cells
as compared to thymidine-treated infected
cells; BUDR-treated infected cells, however,
synthesize viral coat proteins and form viral
particles at approximately the same rate as
the thymidine-treated infected cells (Kaplan
et al., 1965). However, it should be pointed
out that the viral proteins synthesized in the
drug-treated cells may, of course, differ
somehow from normal viral proteins. " (Emph. mine - rjs)
