Postirradiation Properties of a Uv‐sensitive Variant of Cho

Abstract

A UV-hypersensitive mutant of Chinese hamster ovary (CHO) cells, termed 43-38, has been used in a comparative study with the wild type CHO in order to determine the involvement of repair in several postirradiation phenomena. 43-3B has the same growth rate and chromosome number as the wild type CHO-9. It is hypersensitive to UV irradiation (Do of 0.3 J/m2 as compared to 3.2 J/m2 for the wild type). 43-3B shows only about 17% of the UV-stimulated unscheduled DNA repair synthesis of CHO-9 as measured by autoradiography. When breaks in supercoiled chromatin are measured after UV by the nucleoid sedimentation method, the mutant appears to be capable of carrying out only limited incision. A much reduced ability to recover control rates of semiconservative DNA synthesis after UV irradiation was observed in the repair-deficient 43-3B cell line, suggesting that the removal of UVinduced replication blocks by excision repair is the most important factor in allowing recovery of UV-inhibited DNA synthesis. Recovery of colony-forming ability between fractionated UV exposures was observed in the wild type CHO-9, but little recovery was seen in 43-3B. This indicates that excision repair capability can also be important in split-fluence recovery.

CAFFEINE‐ENHANCED PHOTOMOVEMENT IN THE CILIATE, STENTOR COERULEUS

“…The addition of 1 mM caffeine decreases the response times drastically; this effect is partially reversed by the simultaneous application of either LaCIR or ruthenium red. The addition of the Ca2+ ionophore calcimycin (A23187) or the K +ionophore valinomycin likewise reduced the The stop and ciliary reversal in ciliates are thought to be due to a calcium-flux mediated action potential (Thicle et al, 1982;Klumpp and Schultz, 1982;Wood, 1982). Unexpectedly, the latency of the action potential in the control was about 440 ms and thus much longer than the time measured for the phobic response.…”

“…Since the delay time is a prerequisite for a phototactic orientation a shorter response time impairs the phototactic orientation to lateral light. Ca2+ plays only a small role in the resting potential (Wood, 1982), so that the calcium ionophore calcimycin has no such dramatic effect. Thc action potential is broader sirice it may take a longer time f o r the K + counter current t o balance the additional Ca2+ influx.…”

“…Resting and action potentials were recorded in a Faraday cage by standard techniques (Song er at., 1980b;Wood, 1976Wood, , 1982. The glass microelectrodes were prepared on a horizontal puller (PUL-1, W-P Instruments, Inc.), filled with 3 M KC1 under vacuum and mounted on a micromanipulator (MLX, Narishige).…”

IMPAIRED REPAIR OF UVC‐INDUCED DNA DAMAGE IN L5178Y‐R CELLS: DNA UNWINDING STUDIES WITH THE USE OF 1‐β‐D‐ARABINOFURANOSYL CYTOSINE

“…Lehmann, 1982). On the other hand, recovery of ['H]dThd incorporation is delayed in several excision-deficient rodent cells (Hama-Inaba et a/., Wood et al, 1982;Griffiths and Ling, 1984).…”

Molecular cloning and chromosomal localization of DNA sequences associated with a human DNA repair gene.

“…A number of different UV-sensitive mutants have been generated from established cell lines (5,15,23,25,27,30,34). One of these mutant lines, UV-20, isolated from a parental Chinese hamster ovary (CHO) cell line, is sensitive to a number of other DNA-damaging agents, including the DNA cross-linking agent mitomycin C (MM-C) (29).…”