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D L Bentley

Publications and source records attributed to D L Bentley.

50 records · Page 3Linked to original sources
PubMed1982

Unrearranged immunoglobulin variable region genes have a functional promoter.

We have tested whether immunoglobulin light chain variable region genes are capable of directing initiation of transcription without undergoing the DNA rearrangement which creates a complete immunoglobulin gene. Two human Vk genes specifically initiated transcription in vitro at a site which is approximately 30 bases downstream of a TATA box and 20 bases upstream of the initiation codon. A Vk pseudogene which lacks a TATA box at an homologous position was not transcribed to a detectable extent in the in vitro system. One of the Vk genes was injected into Xenopus oocytes and it initiated transcription at precisely the same position as in the HeLa cell extract. It is suggested that the promoter which we have identified upstream of unrearranged Vk genes operates in lymphocytes after V-J joining has occurred to initiate transcription of light chain messenger RNA.

Animals↗
PubMed1982

Localization of human immunoglobulin kappa light chain variable region genes to the short arm of chromosome 2 by in situ hybridization.

The genes for human immunoglobulin kappa light chains have been localized in normal lymphocyte and fibroblast chromosomes by in situ hybridization of probes from cloned DNA fragments of the kappa variable region locus. The localization was achieved by counting grains (after autoradiography) over chromosomes in a number of karyotypes. The variable region gene probes hybridized in a cluster on a region of the chromosome 2 short arm close to the centromere (2cen leads to p12). This location was confirmed in lymphocytes from a balanced translocation carrier 46XXt (2; 16) (q13; q22). Our results show that human kappa light chain genes are located in the region of the break point observed in specific chromosomal translocations associated with Burkitt lymphoma.

Binding Sites, Antibody↗
PubMed1981

Human V kappa immunoglobulin gene number: implications for the origin of antibody diversity.

To assess the relative contributions of germline versus somatically mutated genes in the human immune system, we have examined the size of the kappa light-chain variable region (V kappa) gene pool. Two cloned kappa subgroup 1 (V kappa 1) gene probes detected the same family of 15 to 20 crosshybridizing restriction fragments in human DNA, whereas flanking region probes detected fewer hybridizing fragments. Most of the hybridizing bands represent single-copy genes, as judged by a "'gene titration" experiment. Furthermore, the number of hybridization bands is a good estimate of the haploid gene number, since we observed little polymorphism of restriction sites in the V kappa locus of eight unrelated people. A cloned V kappa 3 probe hybridized to essentially the same 15--20 genes in human DNA as the V kappa 1 probes. These results strongly suggest that a discrete family of 15--20 genes constitutes a large proportion of the V genes from three of the four V kappa subgroups. The small number of V kappa genes in the human genome supports the idea that somatic mutation plays a major role in the origin of antibody diversity in man.

Antibody Diversity↗
PubMed1980

Human immunoglobulin variable region genes--DNA sequences of two V kappa genes and a pseudogene.

The study of immunoglobulin genes at the molecular level can allow us to elucidate the origin of antibody diversity. Investigations of immunoglobulin gene structure in the mouse have shown that light chains are encoded by three gene segments: the C gene encoding the constant region and the V and J genes encoding the variable region. In antibody-producing cells the V and J genes join together to create a complete immunoglobulin gene. No data are available on the structure of human light chain variable region genes, but the variable regions of over 150 human kappa light chain proteins have been sequenced and they comprise four distinct subgroups. Here we report the complete DNA sequences of three human kappa variable region (V kappa) genes isolated from fetal liver DNA. The sequences demonstrate that two non-allelic genes encoding subgroup I proteins have more than 90% nucleotide homology in both proteins coding and non-coding regions. Comparison of these human genes with two complete DNA sequences of mouse V kappa genes shows that V kappa gene structure is highly conserved between the two species, which suggests that V kappa genes rearrange during the differentiation of human lymphocytes by a very similar mechanism to that in the mouse. The sequence of a defective V kappa gene is also described--this gene is unable to code for a functional immunoglobulin due to substitutions, deletions and insertions in its sequence. It is analogous to the pseudogenes of globin and Xenopus 5S RNA.

Animals↗
PubMed1980

The role of gene deletion in the immunoglobulin heavy chain switch.

We have examined the arrangement of the genes for the mouse heavy chain subclasses gamma 2b, gamma 2a and gamma 1 by the Southern hybridisation procedure. Evidence has been found for rearrangement involving the gamma 2b and gamma 2a CH genes in the DNA of cells making IgG2b and IgG2a respectively. The DNA of an IgG2b-secreting line lacks detectable C gamma 1 gene, whilst the DNA of an IgG2a-secreting line lacks detectable C gamma 1 and C gamma 2b genes. The DNA of a cell line secreting IgA lacks detectable C gamma genes. These observations implicate deletion in the mechanism of the H-chain switch and allow a preliminary ordering of some of the CH genes in the mouse genome.

Animals↗
PubMed1980

Confidence interval estimators for parameters associated with quantitative structure-activity relationships.

Use of the "jackknife" as a statistical tool for construction of both point and confidence interval estimators for parameters which are functions of regression coefficients and/or iteratively estimated parameters is described. Examples are presented demonstrating its utility in constructing estimators for log P0 and pi 0 using the parabolic and bilinear quantitative structure-activity relationship (QSAR) models relating nonlinear dependence of activity on hydrophobicity and for log [1/Ki(app)] assuming competitive enzyme inhibition.

Chemical Phenomena↗
PubMed1976

Scanning electron microscopic study of the effects of pressure on the luminal surface of the rabbit aorta.

The effects of pressure on the luminal surface of the rabbit aorta were investigated using the scanning electron microscope. The method followed was perfusion under hydrostatic pressure of a section of thoracic aorta, in vitro. The characteristic ridged pattern seen in sections fixed at zero hydrostatic pressure was to a large extent eliminated when fixation occurred at pressures equivalent to those experienced by the aorta at systole or diastole. This study suggests that the spiral ridged pattern is dependent upon the fixation pressure and may not be present in a normally functioning artery. Any attempts to characterize or interpret the appearance of the luminal arterial wall must take into account the effects of pressure.

Animals↗
PubMedDate not supplied

Most kappa immunoglobulin mRNA in human lymphocytes is homologous to a small family of germ-line V genes.

The mammalian immune system produces 10(6)-10(8) different antibody-combining sites. It has been established that three factors contribute to the diversity of immunoglobulin variable regions: multiple gene segments in the germ line, somatic recombination of these segments and somatic mutation. However, the relative importance of these components in generating the antibody repertoire is unknown. One way to assess the importance of the germ-line component relative to the somatic components would be to determine the number of germ-line V genes expressed. Here, I report that a family of about 25 human germ-line V genes encodes over 50% of kappa mRNA in spleen or peripheral blood lymphocytes. This observation agrees with gene-counting experiments which indicated that the total number of V kappa genes in the human genome is quite small, about 50 or less. Such a small number of germ-line V kappa sequences implies that somatic mutation is the major source of human kappa-chain diversity.

Antibody Diversity↗
PubMedDate not supplied

A block to elongation is largely responsible for decreased transcription of c-myc in differentiated HL60 cells.

The c-myc gene product is a nuclear protein expressed in a wide variety of cell types. It has been implicated in the control of normal cell growth as well as transformation, but its exact function is unknown. When the human promyelocytic leukaemia cell line HL60 is treated with retinoic acid, the cells differentiate into granulocytes, and there is a reduction in steady state c-myc RNA of more than 10-fold. Nuclear runoff assays show that this reduction is caused by a corresponding decrease in the transcription of exon 2. However, only a minor decrease in exon 1 transcription is observed upon differentiation. In undifferentiated HL60 cells there is an approximately 3-fold molar excess of exon 1 transcription over exon 2, and this excess increases to about 15-fold in differentiated cells. This observation suggests that a major component of c-myc transcriptional down-regulation in HL60 cells is at the level of elongation rather than at the level of initiation. The position of the elongation block was mapped to the region of the boundary between exon 1 and intron 1. During HL60 differentiation, a DNase I hypersensitive site in the chromatin about 300 bases downstream of the 5' end of of intron 1 increases in intensity relative to other sites, possibly reflecting events associated with the termination of transcription. Our runoff analysis also revealed transcription of both strands immediately upstream of exon 1 in HL60 cells. The sense strand transcription of this region produces a novel c-myc RNA which initiates several hundred bases upstream of the previously defined promoters and is found in a variety of cell types.

Cell Differentiation↗