The dynamics of antibody-induced redistribution of viral envelope antigens in the plasma membranes of avian tumour virus-infected chick embryo fibroblasts.

Avian tumour virus-infected chick embryo fibroblasts express new antigens, identical with the viral envelope antigens, in their plasma membranes. Electron-microscopic examination of carbon-platinum replicas of cells labelled with haemocyanin-marked antibody has shown the distribution of these antigens to be diffuse over the cell surface with an increased concentration on peripheral cell processes. However, antigen-antibody complexes (AAC), resulting from reaction with specific antibody, may be redistributed into a variety of patterns. Observation of the time course of antibody-induced antigen mobility revealed a rapid and a delayed phase of redistribution. During the rapid phase (10 min or less) some of the antigen-bearing cells reorganized AAC into patches, while the remainder maintained a diffuse distribution. A fraction of the cells with either diffuse or patchy distribution also redistributed AAC into a pattern of 'marginal redistribution (MR)', consisting of linear aggreagation of AAC, at the cell edge. During the 'late' phase of redistribution (after about 20 min), AAC began to condense into one or more foci of coalescence (FC) on each cell. As the number of cells with FC increased with time, the fraction of cells which were labelled decreased. Electron-microscopic observation of thin sections of ferritin-labelled specimens indicated that AAC were lost by endocytosis and that this process was probably related to FC formation. Inhibitors of oxidative phosphorylation, protein synthesis, RNA synthesis, or microtubule assembly had no significant effect on the patterns or the course of redistribution. Iodoacetic acid (IAA), which depletes cellular ATP, and cytochalasin B (CB), which is believed to depolymerize microfilaments, partially inhibited MR and completely prevented FC formation and endocytosis. Paradoxically, IAA or CB-treated cells lost AAC very rapidly by some alternate mechanism not involving FC formation but which may entail a centrifugal migration of complexes to the cell extremities during the process of AAC disposal.     

Evidence that UV-inducible error-prone repair is absent in Haemophilus influenzae Rd, with a discussion of the relation to error-prone repair of alkylating-agent damage.

Haemophilus influenzae Rd and its derivatives are mutated either not at all or to only a very small extent by ultraviolet (UV) radiation, X-rays, methyl methanesulfonate, and nitrogen mustard, though they are readily mutated by such agents as N-methyl-N'-nitro-N-nitrosoguanidine, ethyl methanesulfonate, and nitrosocarbaryl. In these respects H. influenzae Rd resembles the lexA mutants of Escherichia coli that lack the SOS or reclex UV-inducible error-prone repair system. This similarity is further brought out by the observation that chloramphenicol has little or no effect on post-replication repair after UV irradiation. In E. coli, chloramphenicol has been reported to considerably inhibit post-replication repair in the wild type but not in the lexA mutant. Earlier work has suggested that most or all the mutations induced in H. influenzae by NC result from error-prone repair. Combined treatment with NC and either X-rays or UV shows that the NC error-prone repair system does not produce mutations from the lesions induced by these radiations even while it is producing them from its own lesions. It is concluded that the NC error-prone repair system or systems and the reclex error-prone system are different.     

Involvement of membrane sulfhydryls in the activation and maintenance of nutrient transport in chick embryo fibroblasts

At 5 μg/ml, insulin stimulates hexose, A-system amino acid, and nucleoside transport by serum-starved chick embryo fibroblasts (CEF). This stimulation, although variable, is comparable to that induced by 4% serum. The sulfhydryl oxidants diamide (1–20 μM). hydrogen peroxide (500 μM), and methylene blue (50 μM) mimic the effect of insulin in CEF. PCMB-S,¹ a sulfhydryl-reacting compound which penetrates the membrane slowly, has a complex effect on nutrient transport in serum- and glucose-starved CEF. Hexose uptake is inhibited by 0.1–1 mM PCMB-S in a time- and concentration-dependent manner, whereas A-system amino acid transport is inhibited maximally within 10 min of incubation and approaches control rates after 60 min. A differential sensitivity of CEF transport systems is also seen in cells exposed to membrane-impermeant glutathione-maleimide I, designated GS-Mal. At 2 mM GS-Mal reduces the rate of hexose uptake 80–100% in serum- and glucose-starved CEF; in contrast A-system amino acid uptake is unaffected. D-glucose, but not L-glucose or cytochalasin B, protects against GS-Mal inhibition. These results are consistent with the hypothesis that sulfhydryl groups are involved in nutrient transport and that those sulfhydryls associated with the hexose transport system and essential for its function are located near the exofacial surface of the membrane in CEF.