Comparison between mutagenesis in normal and transformed syrian hamster fibroblasts: Difference in the temporal order of HPRT gene replication

A highly tumorigenic subdiploid cell line, BP6T, derived in our laboratory from Syrian hamster embryo (SHE) cells, is amenable to studies of somatic mutation in vitro. Cellular and biochemical characterization of clonally derived BP6T cells resistant to 6-thioguanine (TG^r) or ouabain (Oua^r) demonstrated these mutants to be similar qualitatively to mutants of SHE cells characterized previously (Barrett et al., 1978). BP6T TG^r mutants resistant to 6-thioguanine are cross-resistant to 8-azaguanine, lack HPRT activity, exhibit a low frequency of reversion and arise spontaneously at a rate of 5 × 10⁻⁷ mutants per cell per generation. BP6T Oua^r mutants were shown to be highly resistant to ouabain-mediated inhibition of ⁸⁶Rb influx, indicating an alteration in the Na⁺/K⁺ ATPase. These studies on the BP6T cell line provide the experimental basis for a comparative study of the mutagenic responses of normal, diploid SHE cells versus those of related, but transformed aneuploid cells. Highly synchronized cultures of these 2 cells were mutagenized by pulse treatment with BrdU during different periods of S phase, followed immediately by near-UV irradiation. The induced mutation frequencies so obtained provided information about the temporal order of replication of genes encoding HPRT and Na⁺/K⁺ ATPase in both SHE and BP6T cells. The temporal pattern of replication of Na⁺/K⁺ ATPase gene loci is similar in both cell types, but the temporal order of replication of the HPRT gene is significantly different between SHE and BP6T cells (mid-late S phase, versus early S phase, resp.). This observed difference emphasizes the caution required in the study of mutagenesis and DNA replication using transformed, aneuploid cells under the assumption that the underlying mechanisms are the same for normal, diploid cells.     

Nucleotide sequence of the trpB gene in Escherichia coli and Salmonella typhimurium

We have obtained the entire nucleotide sequence of the penultimate gene of the tryptophan operon, trpB, in Escherichia coli and Salmonella typhimurium. The amino acid sequence deduced for the E. coli gene product is in agreement with earlier, fragmentary protein sequence results. The trpB nucleotide sequences for the two bacterial species are perfectly colinear and show 85% identity. Most of the nucleotide differences found are without consequence for the amino acid sequence, which shows greater than 96% identity. The degree of conservation of both the nucleotide and amino acid sequences is significantly greater than for trpA, the adjacent gene encoding the other subunit of the same enzyme. When synonymous third codon position nucleotide differences are examined, they seem to be distributed at random throughout trpB and trpA, except for one completely conserved 66 basepair long region within trpB.     

The function of tail fibers in triggering baseplate expansion of bacteriophage T4

Normal particles of bacteriophage T4 have six long tail fibers attached to a hexagonal baseplate. T4 particles having various complements of tail fibers were prepared by in vitro addition of fibers to fiberless particles, and the infectivity of the particles was determined. Particles having fewer than six fibers (partially fibered) were found to have a decreased probability of infection. Partially fibered particles having T4 fibers were completed by addition of T6 fibers, and the infectivity was determined on a host that lacked the T6 tail fiber receptor. Attachment of the additional fibers increased the infectivity even though the T6 fibers could not bind to the host cell. The infectivity of particles having mixtures of T4 and T6 fibers was determined on cells having only one type of receptor. The results indicated that particles bound by only three fibers have a low probability of infection. The effect of thermolabile baseplate mutations was also examined. Studies of partially fibered particles and particles with mixtures of fibers indicated that particles with altered baseplates have a less stringent requirement for binding of the tail fibers for infection.     

Ordering tryptophan synthase genes of Pseudomonas aeruginosa by cloning in Escherichia coli.

The Pseudomonas aeruginosa tryptophan synthase genes, trpA and trpB, which are induced by their substrate indoleglycerol phosphate, were cloned along with their controlling region into the BamHI site of pBR322 to produce the 10.7-megadalton plasmid pZAZ5. SalI partial digestion and ligation yielded a smaller plasmid, pZAZ167, with the chromosomal insert reduced in size from 8.1 to 3.4 megadaltons. Both pZAZ5 and pZAZ167 display Pseudomonas-like regulation of the trpA and trpB genes. Deletion of an EcoRI fragment or a BglII fragment from pZAZ167 yielded plasmids pZAZ168 and pZAZ169; the former expresses trpB but not trpA, and the latter has lost both activities. A deleted form of pZAZ5 designated pZAZ101 was obtained by excising a BglII-BamHI segment and religating the trip gene segment in the opposite orientation. This plasmid expresses trpA and trpB constitutively. The physical maps of these plasmids establish the gene order: promoter-trpB-trpA.     

Flavonoid chemistry of arceuthobium (viscaceae)

Flavonoid compounds from 36 of the 38 known taxa of the genusArceuthobium (dwarf mistletoes) were examined. The flavonoid chemistry of the genus is rather uniform, all taxa producing 3-O-glycosides of the flavonols quercetin and myricetin. No infraspecific chemical variation was encountered, and in those instances where subspecific taxa are recognized, their chemistry was uniform. At the subgeneric level, members of subgenusArceuthobium synthesize primarily glucosides, whereas galactosides are more common in subgenusVaginata. In two of the four Old World species of subgenusArceuthobium (A. juniperi- procerae andA. oxycedri) only myricetin 3-O-glucoside was detected. There are no absolute flavonoid differences between subgenera, sections, or series. On the other hand, flavonoids are useful in several instances at the species level. In several cases, chemical data lend support to the recognition of species which in the past have been considered doubtfully distinct on the basis of morphology.     

Farm pond restoration using Chara vulgaris vegetation

Four aged Madison County, New York farm ponds were selected to see if various treatments could be used to restore the water quality. One pond was untreated and used as a control; another pond was partially drained and exposed to the drying and oxidizing effects of the air over the fall and winter; the other two ponds were drained and the accumulated sediment removed by bulldozing. In these latter two ponds, Chara vulgaris vegetation was inoculated following the restoration process. C. vulgaris growth rapidly became the dominant producer where this inoculation was accomplished in the fall of 1976, and it is expected that the other pond will also become a C. vulgaris pond in 1978 — after its oogonia have undergone the requisite winter dormancy period.Early C. vulgaris growth was found to be associated with clear water conditions and lessened phytoplankton growth; short, bushy, light-inhibited growth by the algae stabilized the bottom against wind-caused turbidity because of its rhizoidal growth within the substrate. Pioneer C. vulgaris growth was also found to be highly productive, significantly lowering the pond's CO₂ readings.Investigators of aquatic systems are cautioned to be cognizant of the effect of epiphytic growth on successional events in such environments. Such epiphytes are surely important, if not prime, causes of the demise of various aquatic macrophytes.The partial draining and exposing of a pond over the fall and winter did not yield significantly improved water conditions.     

Systematic relationships in the narrow-leaved species of chenopodium of the Western United States

Brittonia - In a study of ten taxa ofChenopodium occurring primarily in the western United States and designated as the narrow-leaved complex, data from morphology, flavonoid chemistry, and somatic...