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K L Knight

Publications and source records attributed to K L Knight.

At least 37 records · Page 2Linked to original sources
PubMed1999

A role for RAD51 in the generation of immunoglobulin gene diversity in rabbits.

Ig VDJ genes in rabbit somatically diversify by both hyperpointmutation and gene conversion. To elucidate the mechanism of gene conversion of IgH genes, we cloned a rabbit homologue of RAD51, a gene involved in gene conversion in Saccharomyces cerevisiae (yeast), and tested whether it could complement a yeast rad51 mutant deficient in recombination repair. We found that rabbit RAD51 partially complemented the defect in switching mating types by gene conversion as well as in DNA double-strand break repair after gamma-irradiation. Further, by Western blot analysis, we found that levels of Rad51 were higher in appendix-derived B lymphocytes of 6-wk-old rabbits, a time at which IgH genes diversify by somatic gene conversion. We suggest that Rad51 is involved in somatic gene conversion of rabbit Ig genes.

Amino Acid Sequence↗
PubMed1999

44 years of "the journal".

OBJECTIVE: To review the 44-year history of theJournal of Athletic Training. DESCRIPTION: We examined the 179 issues of the Journal and selected 9 years (every 5 years beginning in 1957) for a page-by-page analysis of content. We interviewed 8 former Editors and Editors-in-Chief and drew upon our own experiences during a combined 56 years of association with the Journal. The Journal has undergone significant changes in both structure and quality; its growth mirrors the growth of the athletic training profession. During its infancy, the Journal relied greatly on reprints from other journals. Now, most authors are certified athletic trainers, sharing the results of their own scholarship. CONCLUSIONS: The Journal, like the athletic training profession, is alive and strong. It has become an independent leader in the dissemination of athletic health care information.

Journal Article↗
PubMed1998

Trans-chromosomal recombination within the Ig heavy chain switch region in B lymphocytes.

Somatic DNA rearrangements in B lymphocytes, including V(D)J gene rearrangements and isotype switching, generally occur in cis, i. e., intrachromosomally. We showed previously, however, that 3 to 7% of IgA heavy chains have the VH and Calpha regions encoded in trans. To determine whether the trans-association of VH and Calpha occurred by trans-chromosomal recombination, by trans-splicing, or by trans-chromosomal gene conversion, we generated and analyzed eight IgA-secreting rabbit hybridomas with trans-associated VH and Calpha heavy chains. By ELISA and by nucleotide sequence analysis we found that the VH and Calpha regions were encoded by genes that were in trans in the germline. We cloned the rearranged VDJ-Calpha gene from a fosmid library of one hybridoma and found that the expressed VH and Calpha genes were juxtaposed. Moreover, the juxtaposed VH and Calpha genes originated from different IgH alleles. From the same hybridoma, we also identified a fosmid clone with the other expected product of a trans-chromosomal recombination. The recombination breakpoint occurred within the Smicro/Salpha region, indicating that the trans-association of VH and Calpha genes occurred by trans-chromosomal recombination during isotype switching. We conclude that trans-chromosomal recombination occurs at an unexpectedly high frequency (7%) within the IgH locus of B lymphocytes in normal animals, which may explain the high incidence of B-cell tumors that arise from oncogene translocation into the IgH locus.

Alleles↗
PubMed1998

Dependence of antibody somatic diversification on gut-associated lymphoid tissue in rabbits.

By approximately 4 to 8 wk of age, the IgH VDJ genes of essentially all rabbit B lymphocytes have undergone somatic diversification. Some of this diversification occurs in the appendix, which is a gut-associated lymphoid tissue (GALT). To determine whether GALT is essential for somatic diversification, we surgically removed the appendix, sacculus rotundus, and Peyer's patches from neonatal rabbits (designated GALT-less) and examined the extent to which VDJ genes were somatically diversified. We found that the IgM VDJ genes of peripheral B cells from 2- to 5-mo-old GALT-less rabbits had undergone considerably less somatic diversification than those of control rabbits. Further, the percentage of peripheral B cells in the GALT-less rabbits was generally less than that of controls. Our data suggest that, in rabbits, the primary Ab repertoire develops in GALT, and B cell expansion also occurs there. Hence, GALT may function as a mammalian bursal homologue.

Animals↗
PubMed1998

Differential cleavage of LexA and UmuD mediated by recA Pro67 mutants: implications for common LexA and UmuD binding sites on RecA.

In Escherichia coli, RecA-mediated cleavage of LexA repressor is a key regulatory event required for expression of SOS genes involved in the repair of DNA damage. RecA also mediates the cleavage of UmuD protein to UmuD, a form active in SOS mutagenesis. To determine whether LexA and UmuD have common binding determinants on RecA, we have compared the ability of several recA mutants to function in the cleavage of LexA versus UmuD in vivo. The data reveal that while some recA mutations at Pro67 have a similar effect on LexA and UmuD cleavage, others have striking differential effects. For example, a Pro67-->Trp mutation results in a high level of constitutive cleavage of both proteins. However, Pro67-->Asp and Glu mutations promote constitutive cleavage of LexA and reduce induction of UmuD cleavage to just 5 to 10% of wild-type activity. In contrast, Pro67-->Arg prevents LexA cleavage while allowing nearly 50% of wild-type induction of UmuD cleavage. These results are consistent with the idea that Pro67 is located at a site in the nucleoprotein filament where both LexA and UmuD contact RecA.

Bacterial Proteins↗
PubMed1998

Somatic diversification of IgH genes in rabbit.

Rabbits have helped elucidate one of the major immunologic puzzles, namely the genetic control of antibody diversity. The primary IgH antibody repertoire in rabbits is dominated by B cells that use the same germline VH-gene segment in VDJ gene rearrangements. The VDJ genes of essentially all B lymphocytes undergo somatic diversification within the first few weeks of the rabbit's life. Such diversification occurs both by a somatic gene conversion-like mechanism as well as by somatic hyperpointmutation. The diversification that occurs early in ontogeny takes place in gut-associated lymphoid tissues and potentially depends on external factors such as microbial antigens. Few, if any, new B lymphocytes develop in adult rabbits and we discuss how the antibody repertoire is maintained throughout life. Finally, we discuss the molecular mechanism of somatic gene conversion of Ig genes, including the possibility that this involves the use of RAD51, an enzyme required for gene conversion-mediated mating type switch in yeast.

Animals↗
PubMed1998

Hot-Pack and 1-MHz Ultrasound Treatments Have an Additive Effect on Muscle Temperature Increase.

OBJECTIVE: Therapeutic ultrasound is an effective deep heating modality commonly applied alone or after cooling or heating of the treatment area. The purpose of this study was to examine the tissue temperature rise in the human triceps surae muscle group after ultrasound with prior heating via a silicate gel hot pack. DESIGN AND SETTING: This study was designed as a 2 x 2 x 3 factorial with repeated measures on two factors (depth and time). Independent variables were temperature of pack (hot and room temperature), depth of measurement (1 cm and 3 cm), and time (beginning, after pack application, and after ultrasound). The dependent variable was tissue temperature. Subjects were assigned to one of two treatment groups: ultrasound preceded by a 15-minute hot pack treatment or ultrasound preceded by a 15-minute application with a silicate gel pack at room temperature. Measurements were taken while subjects were treated in a university training room. SUBJECTS: Twenty-one uninjured male and female college student volunteers were randomly assigned to one of the two pack groups. MEASUREMENTS: The hot packs were stored in 75 degrees C water. A 1-MHz ultrasound treatment was administered for 10 minutes at an intensity of 1.5 W/cm(2). Tissue temperature was measured every 30 seconds using 23-gauge hypodermic microprobes interfaced with a telethermometer and inserted 1 and 3 cm below the surface of anesthetized triceps surae muscle. RESULTS: At both tissue depths, there was a 0.8 degrees C greater increase in tissue temperature with hot packs and ultrasound. At 1 cm, ultrasound increased temperature 3.5 degrees C after a 0.5 degrees C rise during the room temperature-pack application, but only 0.6 degrees C after a 3.8 degrees C increase during hot-pack application. At 3 cm, ultrasound increased temperature 3.85 degrees C following a slight (-0.26 degrees C) decrease during the room temperature-pack application and 3.68 degrees C after a 0.74 degrees C increase during hot-pack application. CONCLUSIONS: Vigorous increases in deep muscle temperature (>/=4 degrees C) can be reached with 2 to 3 minutes less total sonation time when preheated with a hot pack. Thus, ultrasound and hot packs have an additive effect on intramuscular temperature, but the characteristics of the additive effect are different, primarily because there appears to be a tissue temperature plateau.

Journal Article↗
PubMed1998

Developing scholarship in athletic training.

OBJECTIVE: To outline the essential elements of scholarship, identify its role in the development of the athletic training profession, and encourage athletic trainers to increase scholarly activities. BACKGROUND: In the process of writing 2 manuscripts for the Journal of Athletic Training about how to write journal manuscripts, we felt something needed to be said concerning why one should write such manuscripts and how individual manuscripts should tie together to advance knowledge. This led us to search the scientific literature for information concerning scholarship and its attainment. Finding no comprehensive discussion on the topic, we then began to investigate components of scholarship and activities that lead to its attainment. DESCRIPTION: Scholarship, knowledge, truth, and theory are defined. The attributes or characteristics of a scholar delineated and discussed include seeking to establish truth and develop new knowledge, developing and refining theory, being focused in one's work, being honest about one's work, communicating ideas and stirring thinking, being open minded, and recognizing the difference between scholarship and pseudoscholarship. It is important to promote scholarship among undergraduate and graduate students; numerous suggestions are outlined. APPLICATION: Scholarship is essential to our survival as a profession. The guidelines presented here will help individuals examine and improve their scholarship.

Journal Article↗
PubMed1997

American Association of Immunologists Presidential Address: doing it together: a perspective on the process of experimental science.

We are witnessing profound changes in how experimental science is done and the rate at which scientists are discovering nature's secrets. While we are experiencing this phenomenal change, we are also at risk, because along with these changes comes the potential for altering the values by which we do science. I share with everyone in our field an abiding concern that scientists of the next generation embrace the values that have guided my generation and the generations of scientists that have preceded me. Because relationships in science are key to passing on these values, I have focused the first part of this address on the importance that relationships have played in guiding my scientific process. In the second part; Looking Toward Our Future, I discuss how the mentoring relationship can serve as an antidote to pressures that threaten our scientific values.

Allergy and Immunology↗
PubMed1997

Somatic hypermutation: mutations 3' of rabbit VDJ H-chain genes.

VDJ genes of rabbit B cells are diversified by a somatic gene conversion-like mechanism in which V(H) gene segments 5' of the VDJ gene serve as donors. To assess whether somatic mutation also contributes to Ab diversification in the rabbit, we searched for mutations 3' of VDJ genes because mutations in this region presumably result from somatic mutation rather than gene conversion. We PCR-amplified and cloned the region extending 534 bp 3' of VDJ genes from splenic DNA of young and adult rabbits. Results of nucleotide sequence analysis of the clones revealed a high mutation frequency (2.4%) within the first 120 bp downstream of VDJ genes. This frequency decreased rapidly with increasing distance 3' of the VDJ genes. The mutations demonstrated both strand bias and dinucleotide preferences characteristic of somatic hypermutation. We conclude that Ab diversity in rabbit is generated not only by somatic gene conversion but also by somatic hypermutation.

Amino Acid Sequence↗
PubMed1997

Allosteric regulation of RecA protein function is mediated by Gln194.

Binding of ATP to the RecA protein induces a high affinity DNA binding required for activation of enzyme function. Screens for in vivo recombination and repressor cleavage activities show Gln194 to be intolerant of all substitutions. Analyses of three mutant proteins (Q194N, Q194E, and Q194A) show that although basal enzyme function is maintained, each protein no longer displays an ATP-induced increase in DNA binding affinity. High salt activation of RecA function is also disrupted by these mutations. In contrast, ATP-induced changes in the oligomeric structure of RecA are maintained in the mutant proteins. These results demonstrate that Gln194 is a critical "allosteric switch" for ATP-induced activation of RecA function but is not the exclusive mediator of ATP-induced changes in RecA.

Adenosine Triphosphatases↗
PubMed1997

IgH gene rearrangements on the unexpressed allele in rabbit B cells.

VDJ genes are assembled in two sequential DNA recombination steps, rearrangement of D and J(H) gene segments followed by rearrangement of a V(H) gene segment. In mouse and human, VDJ gene rearrangements occur in a regulated step in which D rearranges to J(H) on both alleles before V(H) rearranges to DJ. To determine how VDJ gene rearrangements are regulated in the rabbit, we studied the IgH gene rearrangements in rabbit B cells by examining the gene rearrangement on the unexpressed allele in rabbit hybridomas. By Southern blot analysis with probes from the J(H) and 3'V(H)1 regions, we found that approximately 50% of the hybridomas had DJ gene rearrangements on the unexpressed allele, whereas the remaining 50% did not rearrange either J(H) or V(H) genes. Unexpectedly, we found a VD gene rearrangement on the unexpressed allele of a rabbit B cell line, so we PCR-amplified the VD gene rearrangements from splenocyte DNA and found a few VD gene rearrangements in normal B cells as well. The data taken together show that IgH gene rearrangements in rabbit B cells are regulated differently than those in the mouse, and we hypothesize that in some B cells, VDJ gene rearrangements proceed through a VD intermediate rather than through a DJ intermediate.

Alleles↗
PubMed1997

Mutant RecA proteins which form hexamer-sized oligomers.

We have analyzed the oligomeric properties of a number of mutant RecA proteins containing single amino acid substitutions within one region of the subunit interface. In contrast to wild-type RecA, which forms a heterogeneous population of different-sized oligomers, we find that many of these mutant proteins exist in a more homogeneous oligomeric form, which approximates to the size of a RecA hexamer. Some of these mutants have a significant level of activity in vivo for recombinational DNA repair and thus represent the first mutant RecA proteins identified which retain activity yet can exist in a discrete oligomeric state as free protein.

Arginine↗
PubMed1997

Generation of antibody diversity in rabbits.

Most rabbit B lymphocytes use the same VH gene in V(D)J gene rearrangements and undergo somatic diversification by gene conversion and hypermutation. Recent experiments have shown that V(D)J genes in essentially all rabbit B cells diversify shortly after birth and that this diversification occurs in the gut-associated lymphoid tissue. Still to be determined is whether this diversification is developmentally programmed or is driven by exogenous microbial antigens.

Animals↗
PubMed1997

Mutational analysis of the RecA protein L1 region identifies this area as a probable part of the co-protease substrate binding site.

Previous mutational analysis of the L1 region of the RecA protein suggested that Gly-157 and Glu-158 are 'hot-spots' for the occurrence of constitutive LexA co-protease mutants (coprt[c]). In the present study, we clearly establish that position 157 is a hot-spot for the occurrence of such mutants, as 12 of 14 and 10 of 14 substitutions result in this phenotype for UmuD and LexA cleavage respectively. The frequency of such mutations at position 158 is somewhat lower, 8 of 13 and 5 of 13 for UmuD and LexA respectively. Comparison of the UmuD vs. LexA co-protease activity for all single mutants with substitutions at positions 154, 155, 156, 157 and 158 (47 in total) reveals that, although there is good agreement among most mutants regarding their ability to cleave both LexA and UmuD, there are two in particular (Glu-154-->Asp and Glu-154-->Gln) that show a clear preference for cleavage of UmuD. We also show that three second-site mutations that completely suppress coprt(c) activity toward LexA have little or no effect on the coprt(c) activity of the primary mutant toward UmuD. In addition, we observe a high frequency of second-site suppressor mutations, suggesting a functional interaction among side-chains in this region. Together, these results support the idea that the L1 region of RecA makes up part of the co-protease substrate-binding site.

Binding Sites↗
PubMed1997

The effects of selected ankle appliances on postural control.

OBJECTIVE: Although ankle braces supposedly protect the ankle by providing mechanical support of the joint and enhancing proprioceptive input, their proprioceptive effects are unclear. Measuring the center of pressure during posture provides a reasonably well-controlled evaluation of proprioceptive input at the ankle. We, therefore, compared the changes in the center of pressure resulting from wearing ankle braces and wearing no brace (control). DESIGN AND SETTING: Center-of-pressure variables were measured during a one-legged modified Romberg test with six variations. The six test conditions systematically altered the three sensory modalities that control posture: visual input, vestibular input, and proprioceptive input. Subjects performed three 16-second trials of each Romberg variation for each brace condition. SUBJECTS: Twenty-four male volunteers (age = 18 to 26 yr) with no history of ankle injuries in the past 5 years and no difficulty with balance. MEASUREMENTS: Center of pressure, transmitted through the bottom of the foot, was monitored during each trial and transformed into total distance traveled, anterior-posterior (AP) position, and medial-lateral (ML) position. RESULTS: Average AP and ML center-of-pressure positions were increased only during brace wearing when all sensory modalities were functioning normally (control condition). Total center-of-pressure distance was the same for all three brace conditions. CONCLUSIONS: Our results do not support or refute the concept that bracing enhances proprioception. The fact that subjects relocated their center of pressure only during the control condition is perplexing. If braces were to enhance proprioception, one would expect to see lower average ML and average AP center-of-pressure values when comparing the braced with the unbraced conditions. Alternatively, the relocated position may represent a more stable position resulting from enhanced proprioception.

Journal Article↗