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C W Lawrence

Publications and source records attributed to C W Lawrence.

At least 73 records · Page 4Linked to original sources
PubMed1981

Movement of antibody-coated latex beads attached to the spirochete Leptospira interrogans.

Antibody-coated latex beads (Ab-beads) were attached to Leptospira interrogans serovars illini 3055 and icterohaemorrhagiae SC1157. The movement of the Ab-beads relative to the motion of the cells was observed by direct darkfield microscopy or was recorded on videotape. When the Ab-beads were attached to the front end of motile cells, the Ab-beads were displaced towards the back end of the cells. When the cells reversed direction, the Ab-beads also reversed direction. A number of hypotheses were proposed and tested to account for this Ab-bead displacement. The one best supported by the evidence states that the Ab-beads are attached to antigens of the outer membrane sheath. These antigens are dragged laterally through the sheath due to the forward motion of the cells and the retarding forces of the medium acting on the beads. The results obtained provide information on the nature of the outer membrane sheath of L. interrogans, the basis for certain movements of spirochetes, and insight on how spirochetes attach to eukaryotic cells and tissues. In addition, the results indicate that antigens can move laterally through membranes as rapidly as 11 micrometers/sec.

Antibodies↗
PubMed1980

Genetic analysis of gamma-ray mutagenesis in yeast. III. Double-mutant strains.

Comparisons between the 60Co gamma-ray survival curves of diploid strains of the yeast Saccharomyces cerevisiae that are homozygous for two non-allelic radiation-sensitive mutations and the corresponding single-mutant diploids suggest that there are two main types of repair of ionizing radiation damage in this organism. The first, which is defined by the rad52 epistasis group, depends on the activities of the RAD50 through RAD57 genes and is responsible for repairing the larger amount of lethal damage. Previous work [22] shows that this type of repair is essentially error-free. The second, defined by the rad6 epistasis group, depends on the activities of the RAD6, RAD9, RAD18, REV1 and REV3 genes and repairs a smaller, though still substantial, amount of lethal damage. It is also responsible for induced mutagenesis [22, 23]. Data for survival and mutation induction after irradiation in air and partial anoxia show that oxygen-dependent damage can be repaired by either of these two pathways. They also show similar oxygen-enhancement ratios for survival and mutagenesis.

Alleles↗
PubMed1979

Absence of relationship between UV-induced reversion frequency and nucleotide sequence at the CYC1 locus of yeast.

The UV induced mutation frequency of a given base pair located at different sites within the CYC1 gene of Saccharomyces cerevisiae was found to vary by more than fifty fold, indicating the existence of hotspots and coldspots typical of those found in other organisms. We were unable, however, to find any feature of the nucleotide sequence at or near the sites of mutation that explains this variability. These and other data suggest that hotspots are not located within regions particularly susceptible to the formation of premutational lesions. More probably the variation in mutability depends on differences in the activity of enzymes responsible for producing mutations, though the reasons for these differences are not understood and may depend on factors not directly related to nucleotide sequence.

Base Composition↗
PubMed1979

Ultraviolet-induced reversion of cyc1 alleles in radiation-sensitive strains of yeast. III. rev3 mutant strains.

The role of the REV3 gene function in UV-induced mutagensis in the yeast Saccharomyces cerevisiae has been examined by determining the reversion of 12 well-defined cyc1 mutations in diploid strains homozygous for the rev3--1 or rev3--3 allele. The 12 cyc1 alleles include one ochre, one amber, four initiation, two proline missense, and four frameshift mutations. We find that the rev3 mutations reduce the frequency of UV-induced reversion of all of the cyc1 alleles, though different classes of alleles respond to a different extent. These results imply that the REV3 gene function is required for the production of a wide variety of mutational events, though probably not all, and show that each of the three REV loci have different mutational phenotypes. Such diverse phenotypes are not predicted by the unitary model for bacterial mutagenesis (CAILLET-FAUQUET, DEFAIS and RADMAN 1977; WITKIN 1976), suggesting that this is at best an incomplete description of eukaryotic mutagenesis.

Alleles↗
PubMed1979

Genetic analysis of gamma-ray mutagenesis in yeast. I. Reversion in radiation-sensitive strains.

The frequency of revertants induced by 60Co gamma rays of the ochre allele, cyc1-9, has been measured in radiation-sensitive strains carrying one of 19 nonallelic mutations and in wild-type strains. The results indicate that ionizing radiation mutagenesis depends on the activity of the RAD6 group of genes and that the gene functions employed are very similar, but probably not identical, to those that mediate UV mutagenesis. Repair activities dependent on the functions of the RAD50 through RAD57 loci, the major pathway for the repair of damage caused by ionizing radiation, do not appear to play any part in mutagenesis. A comparison between the gamma-ray data and those obtained previously with UV (LAWRENCE and CHRISTENSEN 1976) and chemical mutagens (PRAKASH 1976) suggests that the RAD6 "mutagenic pathway" is in fact composed of a set of processes, some of which are concerned with error-prone, and some with error-free, recovery activities.

DNA Repair↗
PubMed1979

Genetic analysis of gamma-ray mutagenesis in yeast. II. Allele-specific control of mutagenesis.

We find that partially different sets of gene functions are required for the production of different kinds of mutations induced by 60Co gamma rays in Saccharomyces cerevisiae. This observation is very similar to others made previously with respect to UV mutagenesis (LAWRENCE and CHRISTENSEN 1978a,b, 1979) and confirms the conclusion that such distinctive patterns of genetic control reflect properties of the test alleles and their genetic locations, rather than the kinds of lesions required to revert them. The data also support the model of mutagenic repair outlined in the first paper of this series (McKee and LAWRENCE 1979), in which partially different sets of gene functions are required for the production of different kinds of mutations, the formation of mutations at different genetic sites and the induction of mutations by different mutagens.

Alleles↗
PubMed1979

Metabolic suppressors of trimethoprim and ultraviolet light sensitivities of Saccharomyces cerevisiae rad6 mutants.

Dominant mutations at two newly identified loci, designated SRS1 and SRS2, that metabolically suppress the trimethoprim sensitivity of rad6 and rad18 strains, have been isolated from trimethoprim-resistant mutants arising spontaneously in rad6-1 rad18-2 strains of the yeast Saccharomyces cerevisiae. The SRS2 mutations also efficiently suppress the ultraviolet light sensitivity of the parent strains. They do not, however, suppress their sensitivity to ionizing radiation or their deficiency with respect to induced mutagenesis and sporulation. Such observations support the hypothesis that RAD6-dependent activities can be separated into two functionally distinct groups: a group of error-free repair activities that are responsible for a large amount of the radiation resistance of wild-type strains and also for their resistance to trimethoprim, and a group of error-prone activities that are responsible for induced mutagenesis and are also important in sporulation, but which account at best for only a very small amount of wild-type recovery.

Drug Resistance, Microbial↗
PubMed1978

Ultraviolet-induced reversion of cyc1 alleles in radiation sensitive strains of yeast. II. rev2 mutant strains.

The range of specificity of the rev2-1 mutation, an allele that reduces the frequency of ochre revertants induced by UV in Saccharomyces cerevisiae (LEMONTT 1971a), has been investigated by examining its influence on the reversion of eleven well-defined and contrasting cyc1 mutations. We have shown, in support of a suggestion of LEMONTT (1971a), that the REV2 gene product is concerned only with the reversion of ochre alleles; it plays virtually no role in the reversion of amber, missense or frameshift mutations. We have also shown that its effect is specific and confined to only some highly revertible ochre alleles. The REV2 gene product appears to enhance reversion at these sites by facilitating the conversion of two otherwise nonmutagenic photo-products into a single premutational lesion. UV-induced killing of rev2-1 strains was found to be significantly greater on fermentable rather than on nonfermentable media.

Genes↗
PubMed1976

UV mutagenesis in radiation-sensitive strains of yeast.

The yeast Saccharomyces cerevisiae appears to possess a single mutagenic or "error prony" pathway for the repair of UV damage; rev1, rev2, rev3 (Lemontt 1971a), rad6, rad8, rad9 and rad18 (Lawrence et al. 1974; present results). Strains carrying rad6 are the most sensitive to the lethal effects of UV light in this group and double mutants carrying rad6 and either rev1, rev3, rad9 or rad18 are no more sensitive than this single mutant strain, rev3 rad6 doubl- mutant diploids failed to show any UV-induced reversion of the normally highly reversion of the normally highly revertible ochre allele cycl-9, even though a total of more than 2.5 X 10(9) viable cells was examined, suggesting that strains of this kind are entirely UV-immutable; spontaneous revertants could be recovered, however.-The rad6 and rev3 gene products would appear to be necessary for all kinds of mutagenic events at all sites within the genome, but the products of the other genes that act in the "error-prone" pathway have a more restricted role and are involved in the production of only some kinds of mutations. It is suggested that such selectivity arises from the interaction of some repair enzymes with specific nucleotide sequences.

DNA Repair↗
PubMed1975

Influence of repair on the specificity of ultraviolet-induced reversion of an ochre alleles of the structural gene for iso-1-cytochrome c.

The specific action of UV on the reversion of the ochre allele cycl-9, in which 21 out of 23 revertants have been shown to arise from A-T-to-G.C transitions at position one in the UAA codon, was found to depend on the function of the RAD6 gene, since cycl-9 reversion occurred by a variety of single-base-pair substitutions in a strain carrying the rad6-1 allele.

Alleles↗
PubMed1975

Mapping and gene conversion studies with the structural gene for iso-1-cytochrome C in yeast.

We have investigated the order of the four genes cyc1, rad7, SUP4, and cdc8 which form a tightly linked cluster on the right arm of chromosome X in the yeast Saccharomyces cerevisiae. Crossing over and coconversion data from tetrad analysis established the gene order to be centromere-cyc1-rad7-SUP4. Also cdc8 appeared to be distal to SUP4 on the basis of crossovers that were associated with conversion of SUP4. The frequencies of recombination and the occurrence of coconversions suggest that these four genes are contiguous or at least nearly so. Gene-conversion frequencies for several cyc1 alleles were studied, including cyc1-1, a deletion of the whole gene that extends into the rad7 locus. The cyc1-1 deletion was found to be capable of conversion, though at a frequency some fivefold less than the other alleles studied, and both 3:1 and 1:3 events were detected. In general 1:3 and 3:1 conversion events were equally frequent at all loci studied, and approximately 50% of conversions were accompanied by reciprocal recombination for flanking markers. The orientation of the cyc1 gene could not be clearly deduced from the behavior of the distal marker SUP4 in wild-type recombinants that arose from diploids heteroallelic for cyc1 mutations.

Chromosome Mapping↗
PubMed1975

A telefluoroscopic study of lingual contacts made by persons with palatal defects.

Telefluoroscopic tapes were viewed to obtain evaluations of lingual contacts during the production of six consonant sounds by 69 subjects who had a history of cleft palate or velopharyngeal inadequacy. Using phonetic textbook descriptions of normal lingual contacts as standards, these observed contacts were judged to be either normal or deviant in placement, and direction of deviation was noted. Clinical records of subjects afforded medical and surgical histories as well as evaluations of the subjects' intelligibility, nasal resonance and nasal emission at the time of the taping. Evaluations of velopharyngeal adequacy made from these tapes were also available. Based on the results of this study it was concluded that some but not all speakers who have a history of palatal problems use deviant lingual contacts to produce consonant sounds. The use of deviant lingual contacts does not appear to be related to the type of palatal problem, but is significantly related to the adequacy of the velopharyngeal mechanism for speech. Those with adequate mechanisms show the least use of deviant lingual contacts, subjects with borderline adequacy show a greater use, and those with inadequate closure show the greatest use of deviant contacts. There is a significant relationship between the use of deviant lingual contacts and the presence of abnormal intelligibility and abnormal nasal resonance. The tendency toward the use of deviant lingual contacts by those with velopharyngeal insufficiency suggests that these are compensations for the inadequate valving. These compensations may increase both the intelligibility and nasal resonance problems caused by the inadequate valving. Subjects who achieved adequacy of velopharyngeal mechanism for speech before the age of mastery of consonant sounds showed significantly less tendency to use deviant contacts than those who never attained adequacy. This was reflected in intelligible speech and less tendency toward abnormal nasal resonance. It is suggested that when velopharyngeal adequacy cannot be achieved through early surgical intervention, speech therapy may be indicated to promote the development of potentially adequate articulatory patterns and to discourage the development of compensatory mechanisms.

Adolescent↗
PubMed1974

Fine structure mapping in yeast with sunlamp radiation.

The X-ray mapping procedure of Manney and Mortimer (1964) is the most widely applicable and convenient method for fine structure analysis in yeast, but suffers the disadvantage that suitable X-ray machines or gamma ray sources are very expensive. Although many other recombinogens are known, none gives a linear dose-response like X-rays and few are as convenient or give as reproducible results. Experiments with Saccharomyces cerevisiae reported in this paper show, however, that the near-ultraviolet radiation emitted by fluorescent sunlamps gives linear dose-response relations, as reproducible results as ionizing radiations, and map distances which correlate highly with those obtained by using (60)Co gamma rays. It is suggested that this convenient recombinogen may be a suitable low-cost substitute for ionizing radiations in fine structure mapping.

Chromosome Mapping↗