Radiosensitization of primary human tumor cell cultures by N-methylformamide

The effects of the differentiation-inducing agent N-methylformamide (NMF) on the radiation response of ten primary human tumor cell cultures were investigated. Cell survival was determined using an adhesive tumor cell culture system. NMF (1%) was added to cultures on Day 1 and was left for 6 days; cultures were irradiated with graded doses of X rays (1.0-6.0 Gy) on Day 4. Using survival at 2.0 Gy as a comparative endpoint, eight of ten cultures tested exhibited enhanced radiosensitivity upon exposure to NMF. In sensitized cultures, the dose-enhancement factors ranged from 1.3 to 2.5. The NMF-mediated radiosensitization did not appear to be dependent on the histologic cell type. The results presented support previous data obtained from established cell lines and suggest that NMF may offer clinical benefits against a variety of tumor types when used in combination with radiotherapy.

Multiple interactions of a DNA-binding protein in vivo. III. Phage T4 gene-32 mutations differentially affect insertion-type recombination and membrane properties

We have investigated in in vivo roles of T4 gene-32 protein in recombination. We have studied the effects of gene-32 mutations under conditions that allow normal DNA replication and are permissive for progeny production. Under these conditions, certain gene-32 mutations specifically reduce insertion-type (short-interval) recombination but none affect crossover-type (long-interval) recombination (see Figure 5). Heterozygote frequencies in all gene-32 mutants are similar to or higher than in a gene-32+ background and are not correlated with recombination deficiencies. "Recombination-deficient" alleles are dominant or codominant over the "recombination-proficient" gene 32 mutation tsL171. This explains apparent discrepancies between a gene-32 map deduced from two-factor crosses and the map derived from three-factor crosses. We have also found that the "recombination proficient" mutation tsL171 and it homdoalleles suppress the characteristic plaque morphology of rII mutants. Under restrictive conditions, tsL171 is partially suppressed by rII mutations, which allow the use of host ligase in recombination. Our present and previous results are discussed in terms of current recombination models. We conclude that gene-32 protein functions in recombination by forming a complex with DNA, with recombination enzymes and with membrane components. Since gene-32 protein interacts with many components of this recombination complex, gene-32 mutations may differentially affect various recombination steps.

Gene 32 protein of bacteriophage T4 moderates the activities of the T4 gene 46/47-controlled nuclease and of the Escherichia coli RecBC nuclease in vivo

Genes 46 and 47 of phage T4 control a nuclease that is required for genetic recombination and may act similarly to the Escherichia coli RecBC nuclease. In vivo, the nucleolytic activities of both of these nucleases must be moderated so that recombining DNA intermediates are not destroyed. We conclude from our present experiments that the phage T4 gene 32 protein, specifically its C-terminal domain, participates in such moderation. We have investigated DNA degradation in different gene 32 and gene 32/46 mutants under conditions that are completely restrictive for progeny production in all the mutants. Under these conditions, DNA of those gene 32 mutants in which the C-terminal domain of the protein is not synthesized or is modified is degraded to acid-soluble material. T4 gene 46 or E. coli recB mutations reduce such degradation; together they abolish it completely. By contrast, single gene 32 mutants which produce an unaltered C-terminal domain show little or no degradation of their DNA. Residual protection against nucleases is unrelated to residual primary DNA replication or to overproduction of the mutant peptides in the different gene 32 mutants.

Coordinate variation in lengths of deoxyribonucleic acid molecules and head lengths in morphological variants of bacteriophage T4

We have investigated three classes of small bacteriophage T4 particles which differ from normal T4 particles in length of their deoxyribonucleic acid (DNA), in head length, in protein content, and in density. The different particles contain DNA molecules measuring 0.90, 0.77, or 0.67, respectively, of the normal T4 length. An additional class of viable particles contains DNA molecules of 1.1 unit length. These discrete differences in DNA length correspond to discrete differences in length (but not width) of the respective heads and are roughly proportional to the resulting differences in head volumes. The measured relative dimensions of the different heads fit best the relative dimensions predicted by a quasi-icosahedral model in which the smallest T4 head corresponds to an icosahedron with a triangulation number T = 21. The mid-portion of this structure is thought to be elongated by adding successive rows of gene 23 protein hexamers, the normal T4 head having three added rows. Different mutants produce small particles of the three classes in varying proportions, but no mutant produces exclusively particles of a single class. Particles of each class, with indistinguishable DNA content, show additional minor differences in protein content, as measured by differences in buoyant density and in the relative ratio of (32)P to (35)S.