Affiliation:
1. Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111
Abstract
T7 infection of F-factor-containing PIFA
+
,B
+
cells is abortive. In spite of the presence of mRNA for all three classes of T7 proteins, only the earliest of the T7 proteins are synthesized. A crucial question is whether the failure of T7 to develop in PIFA
+
,B
+
cells is the result of an inability to translate the late classes of T7 mRNA or, as has been recently suggested (Britton, and Haselkorn, 1975; Condit, 1975), whether it is the result of a more generalized alteration in membrane permeability. We have examined the effects of the wild-type PIFA
+
,B
+
episome and two episomal mutations (
pifA
−
and
pifB
−
) on in vitro translation and membrane permeability. In vivo the episomal mutations allow partial or complete T7 development to occur. We demonstrate that cell-free protein-synthesizing systems from T7-infected PIFA
+
,B
+
cells show a three- to fivefold decrease in the rate of translation of both natural and synthetic mRNA. In addition, ribosomes from T7-infected PIFA
+
,B
+
cells are defective in their ability to bind Fmet tRNA
f
in response to natural mRNA. By contrast, cell-free extracts from T7-infected
pifA
−
(PIFA
−
,B
+
) cells retain the ability to bind Fmet tRNA
f
and to translate natural and synthetic mRNA at normal rates. The defective T7-infected PIFA
+
,B
+
ribosomes can be restored to full activity by a trypsin-sensitive fraction from uninfected PIFA
+
,B
+
or T7-infected PIFA
−
,B
+
cells. Despite the differences in translational capacity of these extracts, both T7-infected PIFA
+
,B
+
and PIFA
−
,B
+
cells display the same permeability lesions as measured by the loss of ATP from the cells into the supernatant. Mutation of the episome to
pfiB
−
prevents the loss of ATP from the cells after T7 infection.
Publisher
American Society for Microbiology
Subject
Virology,Insect Science,Immunology,Microbiology
Cited by
36 articles.
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