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C C Collins

Publications and source records attributed to C C Collins.

At least 37 records · Page 2Linked to original sources
PubMed1987

Recent progress with the DNA repair mutants of Chinese hamster ovary cells.

Repair-deficient mutants of Chinese hamster ovary (CHO) cells are being used to identify human genes that correct the repair defects and to study mechanisms of DNA repair and mutagenesis. Five independent tertiary DNA transformants were obtained from the EM9 mutant, which is noted for its very high sister-chromatid exchange frequencies. In these clones a human DNA sequence was identified that correlated with the resistance of the cells to chlorodeoxyuridine (CldUrd). After EcoRI digestion, Southern transfer, and hybridization of transformant DNAs with the BLUR-8 Alu family sequence, a common fragment of 25-30 kilobases (kb) was present. Since the DNA molecules used to produce these transformants were sheared to less than 50 kb in size, the correcting gene should be small enough to clone in a cosmid vector. Using drug-resistance markers to select for hybrids after fusion, we have done complementation experiments with ultraviolet light (u.v.)-sensitive mutants and have identified a sixth complementation group, line UV61. Additionally, CHO mutants UV27-1 and MMC-2, isolated in other laboratories, were found to belong to UV group 3, which is represented by line UV24. To study the behaviour of transfected DNA molecules in repair-deficient cells, we treated plasmid pSV2gpt with either u.v. radiation or cis-diamminedichloroplatinum(II) (cis-DDP) and introduced the damaged DNA into normal CHO cells (AA8) and mutants UV4 and UV5. Unrepaired damage to the plasmid was indicated by loss of colony-forming ability of the transfected cells in selective medium containing mycophenolic acid. With u.v. damage, the differential survival of the cell lines was similar to that seen when whole cells are treated with u.v. However, with cis-DDP damage, mutant UV4 did not exhibit the extreme hypersensitivity (50-fold) that occurs when cells are treated. This result suggests that UV4 cells may be able to repair cross-links in transfected DNA.

Animals↗
PubMed1981

Extraocular muscle forces in normal human subjects.

Actively developed horizontal muscle forces and tissue stiffnesses were measured in 29 normal orthophoric volunteer subjects (18 to 33 years old) by means of noninvasive length-tension forceps. Mean active fixation force developed at 50 deg extreme gaze was 26% greater for the medial rectus (74.8 gm) than for the lateral rectus (59.1 gm). The variation of maximum active force among individuals was 2:1 (48 to 103 gm). These muscles developed up to 25% of their maximum active force out of their field of action. Active (counter) hysteresis force differences of over 10 gm were measured between nasal and temporal gaze directions. This study suggests that a muscle which develops a maximum active force of less than 45 gm would be suspect as paretic. Variations from the normal pattern of reciprocal innervation, reflected in the graded active force of individual muscle contraction, may help in understanding some types of oculomotor pathology. The mean tissue stiffness-restraining movement of the globe in the nasal direction (1.05 gm/deg) is 11% greater than in the temporal direction (0.94 gm/deg). This is consistent with a stronger medial rectus balanced by a greater load. Variation of stiffness of 2:1 was observed among individuals; 0.8 to 1.7 gm/deg pulling nasally and 0.77 to 1.2 gm/deg temporally. Passive hysteresis and viscous force differences of over 10 gm were observed between the passive forced pull and normal spring-return of the eye. Large stiffnesses may be normal if balanced by large active forces. Abrupt changes of the length-tension curve indicate the magnitude and location of restrictions.

Adolescent↗
PubMed1979

Microbial transformations and 13C-NMR analysis of colchicine.

Several microorganisms were screened for their ability to biotransform colchicine, and two were selected for preparative scale fermentations. Streptomyces spectabilis and Streptomyces griseus both produced O2-demethylcolchicine and O3-demethylcolchicine but in different amounts. The 13C-NMR assignments of colchicine, O10-demethylcolchicine, and trimethylcolchicinic acid are reported and were used to help identify the structures of the metabolites.

Bacteria↗
PubMed1975

Muscle tension during unrestrained human eye movements.

1. Tensions in the horizontal rectus muscles have simultaneously and continuously been recorded during unrestricted eye movements in four strabismus patients, using force transducers small enough to be implanted in series between the tendons and their points of insertion on the globe. 2. Levels of tension required to maintain fixation at each position of gaze vary from a minimum of 8-12 g approximately 15 degrees outside of muscle's field of action to a maximum of around 40 g at extreme gaze within the muscle's field of action. When tension is plotted as a function of eye position, the static locus of fixation tension levels exhibits a parabolic relationship. 3. Tensions recorded during smooth following movements parallel or slightly exceed those of fixation. 4. At the onset of a saccade, tension in the agonist rises isometrically, then, as the eye moves, tension levels parallel those of fixation but with an isotonic increment of 15-25 g. At the end of the saccadic movement, tension falls essentially isometrically to the new fixation level. 5. Tension in the antagonist reveals an unexpected peak at the onset of a saccade. 6. For saccadic movements tension increments of 15-25 g above the fixation levels suffice to move the eye rapidly to a new position of gaze, regardless of the duration of the saccade and the location of the new fixation point. 7. Maximum and minimum levels of tension during normal fixation, following and saccadic movements, plotted as a function of eye position, form an operational envelope which defines the limits of muscle forces during normal eye movements. The lowest level of this envelope is the parabolic static locus of fixation tensions.

Adult↗