[Antibacterial activity of clindamycin and lincomycin in broth, serum, and in combination with polymorphonuclear leukocytes against Staphylococcus aureus and Staphylococcus epidermidis]

We investigated the antibacterial activity of clindamycin and lincomycin at 1/4 X minimum inhibitory concentration (MIC), 1 X MIC and 4 X MIC against a serum-resistant Staphylococcus aureus and a serum-resistant Staphylococcus epidermidis strain in broth, in serum with and without the presence of leukocytes and in Hank's medium in combination with leukocytes alone. Against both test strains, lincomycin in broth and serum was similarly effective, whereas against S. aureus clindamycin in broth was somewhat more active. In the combined test mixture of serum with leukocytes, even a 1/4 X MIC of clindamycin or lincomycin markedly improved leukocyte killing of S. aureus, whereas both compounds could not further enhance the marked leukocyte killing of S. epidermidis, even at inhibitory concentrations. In Hank's medium with leukocytes alone, clindamycin and lincomycin had at the most only a bacteriostatic effect against both test strains.

[The value of lymphography in testicular, bladder and kidney tumors]

On the basis of 143 lymphographical findings of testicular tumours, 95 of vesical tumours and 55 of renal tumours, this method of examination for urological tumours is evaluated. Lymphography has great diagnostic value for testicular tumours. It is very accurate, and the examination is essential for staging, the planning and checking of therapy and for prognosis. If possible it should always be carried out in combination with computerized tomography. With vesical and renal tumours the value of this examination is often limited by the low lymphogenic rate of metastasis, the low accuracy with vesical tumours and often by therapeutic procedures which are independent of lymph node findings. Nevertheless, even with these two types of tumour lymphography is justified by the information it gives on further course, possible inoperability and the help it gives in field delimitation and checking of therapy. Its use in connection with vesical and testicular tumours will depend on the therapeutic preference of the particular clinician.

[Importance of post-therapeutic computer tomography follow-up studies of patients with malignant testicular tumors]

120 patients with malignant tumours of the testicles were subjected to follow-up studies for up to 7 years after the completion of therapy. In 27 cases (22%) metastases were found, which appeared almost exclusively within the first 3 years after treatment. There was definite evidence of metastasis in 9 out of 46 cases (19%) of seminoma and with 18 out of 74 nonseminomatous tumours.

An X-linked gene affecting mouse cell DNA synthesis also affects production of unintegrated linear and supercoiled DNA of murine leukemia virus

To identify specific cellular factors which could be required during the synthesis of retroviral DNA, we have studied the replication of murine leukemia virus in mouse cells temperature sensitive for cell DNA synthesis (M. L. Slater and H. L. Ozer, Cell 7:289-295, 1976) and in several of their revertants. This mutation has previously been mapped on the X chromosome. We found that a short incubation of mutant cells at a nonpermissive temperature (39 degrees C) during the early part of the virus cycle (between 0- to 20-h postinfection) greatly inhibited virus production. This effect was not observed in revertant or wild-type cells. Molecular studies by the Southern transfer procedure of the unintegrated viral DNA synthesized in these cells at a permissive (33 degrees C) or nonpermissive temperature revealed that the levels of linear double-stranded viral DNA (8.8 kilobase pairs) were nearly identical in mutant or revertant cells incubated at 33 or 39 degrees C. However, the levels of two species of supercoiled viral DNA (with one or two long terminal repeats) were significantly lower in mutant cells incubated at 39 degrees C than in mutant cells incubated at 33 degrees C or in revertant cells incubated at 39 degrees C. Pulse-chase experiments showed that linear viral DNA made at 39 degrees C could not be converted into supercoiled viral DNA in mutant cells after a shift down to 33 degrees C. In contrast, such conversion was observed in revertant cells. Restriction endonuclease analysis did not detect differences in the structure of linear viral DNA made at 39 degrees C in mutant cells as compared to linear viral DNA isolated from the same cells at 33 degrees C. However, linear viral DNA made at 39 degrees C in mutant cells was poorly infectious in transfection assays. Taken together, these results strongly suggest that this X-linked gene, affecting mouse cell DNA synthesis, is operating in the early phase of murine leukemia virus replication. It seems to affect the level of production of unintegrated linear viral DNA only slightly while greatly reducing the infectivity of these molecules. In contrast, the accumulation of supercoiled viral DNA and subsequent progeny virus production are greatly reduced. Our pulse-chase experiments suggest that the apparent, but not yet identified, defect in linear viral DNA molecules might be responsible for their subsequent impaired circularization.

Replication of SV40 chromatin in extracts from eggs of Xenopus laevis

Simian virus 40 (SV40) nucleoprotein complexes were prepared from lytically infected cells and used as primer-templates for DNA replication in protein extracts from Xenopus eggs. We found that nucleoprotein containing replicating SV40 DNA served as primer-template while nucleoprotein with nonreplicating SV40 DNA was ineffective. In vitro DNA synthesis begins with short DNA fragments ("Okazaki fragments") which are, in later steps, joined to give unit length SV40 DNA strands, suggesting that in vivo initiated rounds of replication are completed in vitro in the Xenopus system. This conclusion is supported by a restriction enzyme analysis showing that in vitro DNA synthesis occurs in fragments distal to the SV40 origin of replication. Our studies indicate that SV40 DNA replication in Xenopus extracts can be used an an experimental system to study the biochemistry of replicative DNA chain elongation in vitro.

Replication of simian virus 40 chromatin in vitro depends on the amount of DNA polymerase alpha associated with replicating chromatin

Replication of simian virus 40 (SV40) chromatin in vitro is inhibited by chloride but stimulated by acetate anions even at physiological concentrations of 100-200 mM. In a similar fashion DNA polymerase alpha is affected with respect to the activity with activated DNA as primer template. Furthermore, at concentrations of 100-200 mM acetate DNA polymerase alpha remains associated with replicating chromatin, whereas association is strongly reduced when chloride anions are used at the corresponding concentrations. Thus the salt behaviour of DNA polymerase alpha explains the salt sensitivity of the replication system. Our results confirm the importance of this enzyme for DNA replication.

DNA synthesis: evaluation of a hydrodynamic method for measuring the rate of replication fork movement

When replicating DNA is labeled sequentially with radioactive and density tracers and analyzed by equilibrium centrifugation, the fraction banding at heavier than normal density is inversely proportional to the rate of replication fork movement if there is a sharp transition from one tracer to the other on the newly synthesized chains (Painter and Schaefer, '69). Primate CV-1 DNA labeled for 5 to 30 minutes with 3H-dThd and then for three hours with BrdUrd in the presence of FdUrd bands in a bimodal distribution in alkaline CsCl, rather than in a continuous distribution with a skew toward heavier density seen when FdUrd is omitted and centrifugation is in neutral CsCl. The heavy density peak represents interspersion of both tracers in the DNA and is caused by slow transition from dThd to BrdUrd incorporation when the tracers are switched in the labeling medium. This may result from preferential uptake and incorporation of dThd over BrdUrd. Because of the interspersion, calculation of the rate of replication fork movement is inaccurate. Reversal of the labeling sequence with administration of the long density pulse before the radioactive pulse reduces the problem of interspersion. Using this sequence of labeling, estimates of the rate of fork movement of 0.36-0.38 micrometer/min are obtained when the 3H pulse time is long enough to allow accurate measurement of the fraction of heavy DNA. Analysis by fiber autoradiography yields a rate of 0.56 micrometer/min in the same cell line. If appropriate precautions are taken to minimize mixing of the two tracers in the precursor pool and to ensure that the fraction of heavy DNA is measured accurately, the hydrodynamic technique provides an objective method of measuring rate of fork movement that gives values only slightly lower than those obtained by autoradiography.

Seasonal variation of aryl hydrocarbon hydroxylase inducibility in human lymphocytes in culture

The aryl hydrocarbon hydroxylase (AHH) inducibility in lymphocytes from peripheral blood of 92 healthy young subjects was tested during a period of 8 months (November - June). The average AHH inducibility was found to be higher from March to June than from November to February, indicating a seasonal variation. Various other features of lymphocytes in culture also appeared to change with the season.