A simple mathematical model based on queueing theory is introduced, and used to obtain a sensitive measure of the capacity of a radiation therapy centre to provide service. The model illustrates the relationships among the relevant variables: the patient waiting time, the number on the waiting list, the rate at which requests for radiation therapy are received and the rate at which courses of treatment are commenced. In particular, the rate at which the waiting time increases is equal to the difference between the request rate and the start rate, expressed as a fraction of the start rate, and is therefore a measure of the deficiency in service capacity of a facility. A study of the records of patients treated on the linear accelerators of the Tom Baker Cancer Centre from January 1991 to June 1994 shows that this relationship holds to a high degree of accuracy for average values of the various parameters in spite of the considerable variation in these values, and particularly variation in the individual waiting times. This finding suggests that such an approach would be useful in assessing and comparing the performance of radiation therapy facilities.

The RNA polymerase in cells infected with three group I mutants of vesicular stomatitis virus has been examined. Mouse L cells were incubated at the permissive temperature (30 °C) for a few hours after infection to allow the development of secondary transcription. The temperature dependence of the secondary transcription system was determined from the incorporation of labelled uridine, in the presence of cycloheximide. at 30 and at 38 °C, the latter temperature being non-permissive for viral replication. In cells infected with mutants W14, W28, and G11 at a low multiplicity (20 PFU/cell) secondary transcriptase activity was markedly temperature-sensitive after 3 and 5 h of infection at 30 °C. At a high multiplicity of infection (1000 PFU/cell) cells infected with W28 showed considerable RNA synthesis at 38 °C after 3 h at 30 °C. RNA synthesis was also observed in W28-infected cells in which protein synthesis was allowed to continue after the shift from 30 to 38 °C. In the latter two cases the RNA synthesized contained 12–18S species but little or no 30S mRNA.

The complementation properties of the virus progeny released from cells mixedly infected with mutants of vesicular stomatitis virus belonging to four different complementation groups have been examined. The group IV mutant, tsW16B, was tested in combinations with three group I mutants (tsW4, tsW28, and tsG11), one group II mutant (tsG22), and one group III mutant (tsW29).Virus stocks were grown from isolated plaques appearing on the cell monolayers used to assay the mixed infection yields and tested, in a second series of mixed infections, for their ability to complement each of the two parents. It was found that the virus harvested from each one of the first series of mixed infections contained mutants of both parental types.

When tested in vitro, certain temperature-sensitive (ts) mutants of vesicular stomatitis virus (VSV) belonging to complementation groups I and IV appear to have defects in the virion-bound polymerase. To obtain further information concerning the nature of these defects, representative mutants were dissociated by the method of S. Emerson and R. Wagner (1972), and their supernatant (S) and pellet (P) fractions were tested for transcriptase activity when combined with the P and S fractions, respectively, of VSV-HR virions. It was found that the S fractions from group I mutants tsW4, 11, 14, 15, and 28 were defective in transcriptase activity, whereas their P fractions were as active as those of VSV-HR. On the other hand, the P fraction derived from virions of the group IV mutant tsW16B showed reduced activity at 25 C and very little activity at 38 C. These results suggest that our group I mutants, like those examined by D. Hunt and R. Wagner (1974), have a defect in the soluble transcriptase enzyme, whereas mutant tsW16B (group IV) has a defect in a sedimentable component required for transcriptase activity, possibly in the ribonucleoprotein template.

SUMMARY Reciprocal complementation experiments in mouse L cells and BHK-21 cells show that the complementing temperature-sensitive (ts) mutants of vesicular stomatitis virus (VSV), Indiana serotype, isolated from the hr wild-type strain, belong to groups I, III and IV (Flamand & Pringle, 1971). Since the homologies of ts mutants isolated from three different wild-type strains growing in different host cells can be established by cross-complementation, proposals are made for a uniform nomenclature of ts mutants of VSV Indiana.

Some thirty mutants of vesicular stomatitis virus have been isolated which replicate normally in culured mouse L cells at 30 degrees C but, unlike wild-type virus, fail to do so at 38 degrees C. When certain pairs of mutants are used in mixed infections they are able to 'complement' each other, i.e. produce virus at 38 degrees C, suggesting that their defects are in different genes. It has been possible to assign some of the mutants unambiguously to three complementation groups and representatives of each of these groups have been tested for their ability to synthesize viral RNA at 30 degrees C. In Group I mutants there is some viral RNA synthesis but it can all be attributed to the RNA polymerase contained in the virus particles. Group II mutants synthesize RNA at a rate comparable to that of the wild type. In Group III mutants, viral RNA synthesis is completely suppressed at 38 degrees C, apparently due to a temperature-sensitive defect in the structural polymerase.

The temperature dependence of the virion-associated polymerase activity of six temperature-sensitive (ts) mutants of vesicular stomatitis virus (tsW10, 11, 14, 16B, 28, and 29) has been examined in vitro and compared to the heat-resistant parent (HR). The polymerase of five of the mutants (tsW10, 11, 14, 16B, and 28) appears to be significantly more ts than that of HR. Because certain pairs of these five mutants can complement each other's in vitro polymerase activity, it appears that in vitro some components involved in the polymerase of one virion can be utilized by another virion. Examination of 19 revertants of tsW11 and tsW16B which had regained their ability to replicate at 38 C showed that their in vitro polymerase activity had also become less ts. Furthermore, it was found that the pairs of mutants which showed in vitro complementation of polymerase activity at 38 C were those which had shown complementation in yielding infectious progeny in mixedly infected cells. These two observations suggest that the ts behavior of the in vitro polymerase activity of the five mutants is related to their inability to replicate at the nonpermissive temperature.

The complementation properties of 25 temperature-sensitive mutants of VSV have been tested by measuring the yield of virus in mixedly infected cells at the nonpermissive temperature, 38°C. Two of the mutants, ts10W and ts16BW, complement all the mutants except each other and therefore form one distinct complementation group, A. Two other mutants, ts12W and ts29W do not complement each other but complement nearly all the other mutants and have been assigned to a second complementatation group, B. A group of six mutants, all of which show an increased heat lability of the virion, show no complementation within the group and have been assigned to a third group, C. Most of the remaining mutants complement at least one member of each of groups A, B, and C but have not yet been assigned to other groups since many of the crosses of these mutants with group C mutants fail to show complementation. Virus-specific RNA synthesis in L cells infected with the various mutants was investigated by measuring the incorporation of 14C-labeled uridine. All the group C mutants show little or no virus-specific RNA synthesis at 38°C, even at high multiplicities, suggesting that in these mutants the defect is in the structural RNA polymerase. The two mutants of group A show little or no virus-specific RNA synthesis at 38°C at low input multiplicities but considerable RNA synthesis at high multiplicities. Since this synthesis is not reduced by the presence of puromycin it would appear that these mutants have a structural polymerase which is functional at 38°C but are defective in some other type of RNA synthesis. Mutants of group B show RNA synthesis at 38°C comparable to that of the wild type at all multiplicities but fail to produce infectious virus after a shift from 30 to 38°C at any time during the growth cycle. The defect in these mutants therefore appears to be in some function such as the synthesis or assembly of structural proteins.

Microbiology Society journals contain high-quality research papers and topical review articles. We are a not-for-profit publisher and we support and invest in the microbiology community, to the benefit of everyone. This supports our principal goal to develop, expand and strengthen the networks available to our members so that they can generate new knowledge about microbes and ensure that it is shared with other communities.

Twenty-four mutants of vesicular stomatitis virus have been isolated. These mutants replicate normally at 30°, but at 38° the yield is much reduced. In contrast to results reported for some other animal viruses, only one mutant showed evidence of RNA synthesis at 38°. The mutants were also characterized by the effects on viral yield and on RNA synthesis of a temperature shift from 30° to 38° at various times during the replicative cycle. In one group of mutants the defect appears to prevent the onset of RNA synthesis, and in another group the defect appears to interfere directly with RNA synthesis. In one mutant, ts4, there is a structural defect in the virion which, in cells infected and incubated at 38°, apparently prevents the initiation of RNA synthesis but does not interfere directly with the incorporation of the altered structural component into progeny virions. Even at 38° all the mutants caused a marked inhibition of cellular RNA synthesis comparable to that produced by the wild type.

Kononenko (1958), assuming a constant LET for α particles, derived factors from which the average dose in a cylindrical cavity surrounded by an α emitter was calculated. The agreement between his experimental and theoretical data has been used as indication of the usefulness of the constant LET approximation for α particles (Spiers, 1966). The model of α-particle passage through matter used by Kononenko had the following properties: (a) α particles travel in straight paths for distances equal to their track lengths, (b) α-particle LET is constant and equal to (initial energy/ track length).

The addition of inositol to the yeast Saccharomyces cerevisiae protects the yeast—when suspended in air—against death from desiccation, ultra-violet light and X-rays.