PubMed Health⌕ Search

Biomedical subjects

J G Roan

Publications and source records attributed to J G Roan.

14 recordsLinked to original sources
PubMed1999

Saccharomyces cerevisiae RNA polymerase I terminates transcription at the Reb1 terminator in vivo.

We have mapped transcription termination sites for RNA polymerase I in the yeast Saccharomyces cerevisiae. S1 nuclease mapping shows that the primary terminator is the Reb1p terminator located at +93 downstream of the 3' end of 25S rRNA. Reverse transcription coupled with quantitative PCR shows that approximately 90% of all transcripts terminate at this site. Transcripts which read through the +93 site quantitatively terminate at a fail-safe terminator located further downstream at +250. Inactivation of Rnt1p (an RNase III involved in processing the 3' end of 25S rRNA) greatly stabilizes transcripts extending to both sites and increases readthrough at the +93 site. In vivo assay of mutants of the Reb1p terminator shows that this site operates in vivo by the same mechanism as has previously been delineated through in vitro studies.

Base Sequence↗
PubMed1984

Variations in transcriptional activity of rDNA spacer promoters.

We have compared the DNA sequences of several different examples of the duplicated polymerase I promoters that are found in rDNA spacers of Xenopus laevis. Although different spacers exhibit different amounts of transcription in vivo, this does not seem to be due to DNA sequence differences between spacer promoters. We have found that several different spacer promoters when subcloned and injected into oocytes exhibit similar promoter activities when transcription is assayed by primer extension analysis. Moreover, the activity of these spacer promoters is the same as that of a co-injected gene promoter. The equivalence of spacer promoter activity and gene promoter activity was also found when rDNA plasmids containing intact spacers were injected into oocytes and transcription assayed by primer extension. This is in contrast to (1) the inactivity normally exhibited by the promoters of endogenous spacers in oocytes, (2) the relative inactivity of spacer promoters found when transcription of the same rDNA plasmids is assayed by electron microscopy.

Animals↗
PubMed1984

The mechanism of nucleolar dominance in Xenopus hybrids.

We have mimicked the phenomena of nucleolar dominance by injecting cloned ribosomal genes from X. laevis and X. borealis into oocytes from either species and into embryos. The results of these experiments suggest that the dominance of the laevis ribosomal genes in hybrid embryos is primarily due to the fact that the laevis spacer has more copies of an enhancer element for the ribosomal gene promoter than does the borealis spacer. A contributing effect is that the laevis promoter functions well with transcription machinery from either species while the borealis promoter interacts poorly with laevis transcription machinery.

Animals↗
PubMed1983

Spacer regulation of Xenopus ribosomal gene transcription: competition in oocytes.

Xenopus laevis ribosomal gene plasmids bearing different length spacers were injected into oocyte nuclei in competition with each other. The spacer has two basic effects on transcription from the gene promoter. First, if the competing pair have unequal spacer lengths, the gene promoter attached to the longer spacer is always dominant in transcription (the competition effect). Second, as the total amount of spacer in the reaction increases, the total amount of transcription decreases (the sink effect). Both the competition and the sink effect are attributed to sequence elements that are 60 or 81 bp long, which are present in multiple copies in the spacer and are related in sequence to part of the gene promoter. The 60/81 bp elements confer competitive dominance in either orientation. A model which explains both the competition and the sink effects is discussed in which the 60/81 bp elements are attraction sites for a factor(s) which is needed to activate the gene promoter.

Animals↗
PubMed1980

Response of lymphocytes from lead, cadmium, and methylmercury exposed mice in the mixed lymphocyte culture.

Mice were exposed to various dosages of lead, cadmium, or methylmercury for 10 weeks. At the end of the feeding trial, splenic lymphocytes were evaluated for responsiveness in mixed lymphocyte cultures. Cadmium and methylmercury as well as one dose level of lead tended (not significant) to stimulate the lymphocyte reaction. These results are discussed and compared to other investigations concerned with the effect these environmental contaminants have on the cell mediated immune response of animals.

Animals↗
PubMed1980

Effects of lead, cadmium and methylmercury on immunological memory.

The memory response of lymphocytes to antigen was altered in mice exposed to lead, cadmium, or methylmercury. Both lead (1300 ppm) and methylmercury(10 ppm) impaired the memory response while cadmium (300 ppm) stimulated memory. Memory was significantly affected only at the largest dosages where toxic signs were generally detected. The lower dosages did not affect the memory of lymphocytes which produce antibody. These data suggest that the T lymphocyte rather than the B lymphocyte is the cell affected when the secondary immune response is altered after exposure to subclinical amounts of these environmental contaminants.

Animals↗
PubMed1979

Evaluation of data from mitogen studies in CBA mice: comparison of counts per minute, stimulation index and relative proliferation index.

Lymphocyte proliferation assays were conducted on splenic lymphocytes collected from CBA mice that had been exposed to lead acetate or cadmium chloride for 10 weeks. The ability of mitogens concanavalin A and lipopolysaccharide, as well as purified protein derivative, to induce proliferation in vitro in the presence or absence of macrophages was assessed. Data were compared by using counts per minute (cpm), stimulation index, and relative proliferative index. Data varied considerably within treatment groups performed on different days, which is a typical characteristic of mitogen proliferation investigations. According to cpm data, only 3 of 21 treatments were significantly (P less than 0.05) altered when compared with controls. The stimulation indices were highly influenced by background counts and frequently did not correlate with cpm. The relative proliferative index, on the other hand, calculates net cpm, closely corresponds to cpm, compensates for background counts and is affected less by variation than is the stimulation index, and selected cutoff values give a more sensitive measure for determination of altered proliferative responses when statistical procedures are not applicable. Effects of macrophages, carbon dioxide, and bovine fetal serum on lymphocyte transformation are discussed.

Animals↗
PubMed1977

Immune response in aged mice exposed to lead.

Mice were exposed to 0, 13, or 1,300 ppm lead in drinking water for 18 months. The immunological assays examined were mitogen (lipopolysaccharide E. coli, concanavalin A, and phytohemagglutinin-P) stimulation of lymphocytes; erythrocyte-antibody (EA), erythrocyte-antibody-complement (EAC), and phagocytosis of macrophages; and EAC of splenic lymphocytes. As measured by the majority of these assays, the low dosage (13 ppm) of lead tended to stimulate certain immune responses (lymphocyte mitosis, EA, and EAC) while the high dosage (1,300 pm) did not provoke an appreciable alteration. The results were interpreted by comparing data on aged mice with data on young adult mice. It was apparent from this comparison that the aged mice were naturally immunosuppressed. Therefore, the results obtained from lead-exposed mice were unpredictable.

Aging↗
PubMed1976

Humoral antibody response in mice after single dose exposure to lead or cadmium.

A single dose of lead administered orally or intraperitoneally (IP) to mice stimulated formation of IgM antibody. Cadmium caused an increase in IgM antibody formation when injected ip but resulted in a slight decrease when given orally. Lead, orally or ip, significantly reduced IgG antibody but the IgG antibody response decreased only when cadmium was given orally and increased when injected ip. Since responses vary according to route of administration, experiments should be designed so that experimental exposure will simulate natural exposure in order to develop comparable data.

Administration, Oral↗
PubMed1975

Antibody suppression by cadmium.

Mice exposed to subclinical doses of cadmium chloride for ten weeks and inoculated with antigen six weeks after discontinuance of exposure had a remarkable decrease in antibody-forming cells, particularly IgG. These results indicate that immunosuppression produced by environmental contaminants may persist for several months after exposure to the contaminant.

Animals↗
PubMedDate not supplied

Methylmercury: effects on B-lymphocyte receptors and phagocytosis of macrophages.

Mice were exposed to 0, 1,5 and 10 ppm methylmercury for 10 weeks. After exposure, splenic lymphocytes were collected and examined for the ability of their antibody (Fc) and complement receptors to rosette sheep red blood cells (SRBC) in the presence of anti-SRBC antibody. Peritoneal exudate cells were also collected and examined for Fc rosetting and phagocytic properties. The largest dosage of methylmercury activated the complement receptor of B lymphocytes to rosette SRBC. The lower dosages did not affect this property of B cells nor did methylmercury alter the Fc receptors on B lymphocytes and macrophages or phagocytosis of peritoneal macrophages.

Animals↗