Isolation and purification of large quantities of DNA replication intermediates by pH step alkaline elution.

The alkaline elution technique has been modified to be used in the isolation of DNA replication intermediates and in the study of the process of DNA replication. In this procedure pulse labeled CHO cells are layered onto a membrane filter, lysed with detergent, and the nascent DNA eluted in step-wise fashion with tetrapropylammonium hydroxide at pH 11.0, 11.

Measurements of DNA damage in Chinese hamster cells treated with equitoxic and equimutagenic doses of nitrosoureas.

The DNA of V-79 Chinese hamster cells was examined by alkaline elution following treatment of cultures with eight different nitrosoureas. Drug incubations were performed under consistent biological conditions of equal toxicity and equal mutation induction at the hypoxanthineguanine phosphoribosyltransferase locus. The goals of this study were to determine whether DNA damage could be detected in cells treated with biologically relevant doses of nitrosoureas and to determine whether the type and number of observed DNA lesions could be correlated with the cytotoxic and mutagenic effects of the drugs.

Postoperative ileus: a colonic problem?

Postoperative electromechanical activity of the gastric antrum, small bowel, right colon, and sigmoid colon was recorded in stumptail monkeys in response to retroperitoneal dissection and transient clamping of the renal pedicle. Bipolar silver electrodes and extraluminal bonded strain gauge transducers were used to record slow-wave and spike discharges and contractions of intestinal smooth muscle. After operation myoelectric activity was decreased transiently in the antrum and for only a few hours in the small bowel.

Non-enzymatic DNA strand breaks induced in mammalian cells by fluorescent light.

Fluorescent light (5.4 J . m-2 .

Differential repair of 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea-induced DNA damage in two human colon tumor cell lines.

Two human colon tumor cell lines were examined for their responses to 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea treatment when maintained as cultured cell lines and xenograft tumors in nude mice. One tumor line, HT, was resistant to 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea treatment both in tissue culture and in vivo. The other tumor line, BE, was sensitive to 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea treatment in vitro and in vivo.

Differential inhibition of the rejoining of X-ray-induced DNA strand breaks in normal and transformed human fibroblasts treated with 1,3-bis(2-chloroethyl)-1-nitrosourea in vitro.

The effects of 1,3-bis(2-chloroethyl)-1-nitrosourea on the rejoining of X-ray-induced DNA strand breaks were examined in normal human fibroblasts (WI-38) and a simian virus 40-transformed derivative (VA-13) with the use of alkaline sucrose sedimentation. 1,3-Bis(2-chloroethyl)-1-nitrosourea was capable of partially inhibiting repair of X-ray-produced DNA strand breaks in both cell types when the drug was added to the culture medium immediately after X-irradiation. However, when 1,3-bis(2-chloroethyl)-1-nitrosourea exposure preceded X-ray by 1 hr, DNA repair was inhibited to a much greater extent than it was when 1,3-bis(2-chloroethyl)-1-nitrosourea followed X-ray.

Hydrocarbon uptake in hydrocarbon fermentations.

Candida lipolytica (strain ATCC 8662) was grown on a simple defined medium with n-hexadecane as the main carbon source under batch fementation conditions. The relative importance of the cells growing in the aqueous phase on the overall kinetics was studied. The effect of interfacial tension, unoccupied interfacial area, and pseudosolubility on the specific growth was also studied.

Oxygen transfer and axial dispersion in an aeration tower containing static mixers.

Oxygen transfer from gas to liquid under steady-state cocurrent flow conditions was modeled using the dispersion model, and the oxygen transfer coefficients were estimated from available data for a column with Koch motionless mixers. The dispersion in the column was estimated for several different gas and liquid flow rates using steady-state tracer experiments. The estimated oxygen transfer coefficients were compared with those estimated using complete mixing and plug flow models.

Characteristics of hydrocarbon uptake in cultures with two liquid phases.

In hydrocarbon fermentation, the efficiency of hydrocarbon uptake by cells is one of the keys to the economical production of single-cell protein. This work is concerned with characterization of cultures with two liquid phases for understanding the hydrocarbon uptake process by cells. Batch cultivation of Candida lipolytica was carried out in shaking flasks and in a tower fermentor with motionless mixers.

Normal DNA strand rejoining and absence of DNA crosslinking in progeroid and aging human cells.

We have measured by alkaline elution and alkaline sedimentation the rate of rejoining of X-ray induced DNA single-strand breaks in terminally senescent cultured WI-38 cells. Using the alkaline elution method, we have also measured the rate of ligation in cultured progeroid cells. In both cells and by both methods of measurement the rates of strand rejoining were normal.

Fractionation of DNA from mammalian cells by alkaline elution.

The method of alkaline elution provides a sensitive measure of DNA single-strand length distribution in mamalian cells and is applicable to a variety of problems concerning DNA damage, repair, and replication. The physical basis of the elution process was studied. The kinetics of elution above the alkaline transition pH were found to occur in two phases: an initial phase in which single-strand length is rate limiting, followed by a phase in which elution is accelerated due to the accumulation of alkali-induced strand breaks.

Replication of DNA in mammalian chromosomes. III. Size and RNA content of Okazaki fragments.

A study of sedimentation and buoyant density of Okazaki fragments from mammalian chromosomes along with electron microscopic studies indicate that fragments from about 200 to 1200 nucleotides long may have RNA segments covalently attached. The fragments in some CsCl isopycnic gradients banded in two rather distinct bands. One band corresponds to the density of single-stranded DNA, but the other has a higher buoyant density which could be conferred by a segment of RNA up to 180 nucleotides or more in length.