PubMed Health⌕ Search

Biomedical subjects

S C Cheng

Publications and source records attributed to S C Cheng.

At least 55 records · Page 3Linked to original sources
PubMed1993

Yeast precursor mRNA processing protein PRP19 associates with the spliceosome concomitant with or just after dissociation of U4 small nuclear RNA.

During assembly of the spliceosome, the U4 small nuclear RNA (snRNA) interacts with the spliceosome as a preformed U4/U6-U5 triple small nuclear ribonucleoprotein (snRNP) complex. Subsequently, U4 becomes loosely associated with the spliceosome, whereas U5 and U6 remain tightly associated, suggesting unwinding of the U4/U6 duplex. We show that this step of the assembly process can be blocked by limiting the ATP concentration in the splicing reaction. We also show that the yeast precursor mRNA processing protein PRP19 becomes associated with the spliceosome during this transition. Thus, PRP19 may function in this step of spliceosome assembly.

Adenosine Triphosphate↗
PubMed1993

Assessment of the effects of instrumentation, monoclonal antibody, and fluorochrome on flow cytometric immunophenotyping: a report based on 2 years of the NIAID DAIDS flow cytometry quality assessment program.

This study of the effect on CD4%, CD8%, CD3+8+%, and CD3% of flow cytometer, monoclonal antibody, and fluorochrome was based on 71 whole-blood samples, each evaluated by 42 to 59 laboratories during 2 years of a flow cytometry quality assessment program. For the 24 HIV-positive specimens, FACScans produced significantly lower CD4% values than EPICS-Cs or EPICS Profiles, and for the 47 HIV-negative specimens, FITC was associated with significantly lower CD4% values than PE or RD1, but differences were never larger than 2% and regressions accounted for only 3-12% of the variability. The labs using the most common CD4 technique had significantly higher between-laboratory variability than all other labs grouped together. For both CD8 and CD3+8+, measurements on FACScans were significantly higher than measurements on EPICS, and measurements using Leu2 were significantly higher than measurements using T8, with regressions accounting for 12-31% of the variability. The machine differences in medians were 3-7% for labs using Leu2-FITC. It might be worthwhile to discourage the use of Leu2-FITC for measuring CD8% but no change in instrument, monoclonal antibody, or fluorochrome would greatly improve interlaboratory agreement on CD4%.

Antibodies, Monoclonal↗
PubMed1993

Effect of irrigation fluids on the articular cartilage: a scanning electron microscope study.

Four irrigation solutions, two for general arthroscopic examination and two for electrosurgery, were evaluated for their effects on the ultrastructure of the articular cartilage surface using an animal model with a scanning electron microscope (SEM). The murine knee joints were irrigated continuously for 1 or 2 h with normal saline, Ringer's lactate, 3% sorbitol, or distilled water, respectively. The articular cartilage of the patella was evaluated in situ; that is, the cartilage was kept intact as it related to the underlying bone tissue, so that artifacts during the biopsy procedure could be prevented. Results of the study showed no significant differences among the four solutions and the unirrigated control group. We conclude that Ringer's lactate, normal saline, distilled water, and 3% sorbitol can all be safely used as irrigation solutions in arthroscopic surgery.

Animals↗
PubMed1993

Serum levels of soluble CD8, neopterin, beta 2-microglobulin and p24 antigen as indicators of disease progression in children with AIDS on zidovudine therapy.

OBJECTIVE: To test the hypothesis that serum levels of soluble markers in children change after initiation of zidovudine therapy and that the extent and pattern of these longitudinal changes correlates with clinical outcome. PATIENTS AND METHODS: We measured serum levels of soluble CD8, neopterin, beta 2-microglobulin (beta 2M), and p24 antigen, and CD4 cell counts, before the initiation of zidovudine therapy and at 12, 24 and 48 weeks of treatment in 24 HIV-1-infected children (Centers for Disease Control classification P2) and 15 controls. RESULTS: Soluble CD8 levels were elevated before therapy in 70% of the infected children; subsequent decreases were associated with lower risk of disease progression. The mean serum neopterin level before treatment was elevated in infected children; decreases in neopterin levels marginally reflected improved or stable clinical status. Serum beta 2M levels and CD4+ cell counts were not associated with clinical outcome. Only 10 out of the 24 patients had detectable levels of serum p24 antigen before treatment; again, the amount of decline after initiation of therapy did not predict clinical outcome. CONCLUSION: Decreasing levels of soluble CD8 and neopterin in HIV-1-infected children receiving zidovudine therapy might reflect a good response to treatment and a slowing of disease progression.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Prediction of CD4 count from CD4 percentage: experience from three laboratories.

OBJECTIVE: CD4 counts have been used to monitor progression of disease in HIV infection as criteria for initiation of therapy, and to stratify and follow patients in clinical trials. Recently, the Centers for Disease Control and Prevention (CDC) has made CD4 counts part of the classification of HIV disease. Because a CD4 percentage may be the only laboratory information available, this study was initiated to determine whether the correlation between CD4 percentages and CD4 counts is sufficiently high to enable these measures to be substituted for each other. DESIGN, SETTING AND PATIENTS: One thousand consecutive CD4 measurements from the University of Washington (UW) were used to create a model that was tested using datasets of 1000 CD4 measurements each from Maryland Medical Laboratories (MML) and Rush-Presbyterian-St Luke's Medical Center (Rush). The patients were not selected for age, sex, risk group or treatment. All patients from MML and Rush were known to be HIV-positive, while the HIV status of all UW patients was unknown. RESULTS: The model predicted that a patient with a CD4 percentage > or = 14% would have a CD4 count > or = 200 x 10(6)/l(if CD4 percentage of 14% was used, 9% of patients would have a CD4 count > or = 200 x 10(6)/l), and a patient with a CD4 percentage > or = 27% would have a CD4 count > or = 500 x 10(6)/l(if CD4 percentage of 27% was used, 17% of patients would have a CD4 count > or = 500 x 10(6)/l). CONCLUSIONS: These CD4 percentage correlations may be useful when a white blood cell and lymphocyte count are not available to calculate the CD4 count.

CD4-Positive T-Lymphocytes↗
PubMed1993

PRP19: a novel spliceosomal component.

We have isolated the gene of a splicing factor, PRP19, by complementation of the temperature-sensitive growth defect of the prp19 mutant of Saccharomyces cerevisiae. The gene encodes a protein of 502 amino acid residues of molecular weight 56,500, with no homology to sequences in the data base. Unlike other PRP proteins or mammalian splicing factors, the sequence of PRP19 has no discernible motif. Immunoprecipitation studies showed that PRP19 is associated with the spliceosome during the splicing reaction. Although the exact function of PRP19 remains unknown, PRP19 appears to be distinct from the other PRP proteins or other spliceosomal components.

Amino Acid Sequence↗
PubMed1993

The yeast PRP19 protein is not tightly associated with small nuclear RNAs, but appears to associate with the spliceosome after binding of U2 to the pre-mRNA and prior to formation of the functional spliceosome.

We have previously shown that the yeast PRP19 protein is associated with the spliceosome during the splicing reaction by immunoprecipitation studies with anti-PRP19 antibody. We have extended such studies by using extracts depleted of specific splicing factors to investigate the step of the spliceosome assembly process that PRP19 is involved in. PRP19 was not associated with the splicing complexes formed in U2- or U6-depleted extracts but was associated with the splicing complex formed in heat-inactivated prp2 extracts. This finding indicates that PRP19 becomes associated with the splicing complexes after or concomitant with binding of the U6 small nuclear ribonucleoprotein particle (snRNP) to the precursor RNA and before formation of the functional spliceosome. We further analyzed whether PRP19 is an integral component of snRNPs. We have constructed a strain in which an epitope of nine amino acid residues recognized by a well-characterized monoclonal antibody, 12CA5, is linked to the carboxyl terminus of the wild-type PRP19 protein. Immunoprecipitation of the splicing extracts with anti-PRP19 antibody or precipitation of the extracts prepared from the epitope-tagged strain with the 12CA5 antibody did not precipitate significant amounts of snRNAs. Addition of micrococcal nuclease-treated extracts to the PRP19-depleted extract restored its splicing activity. These results indicate that PRP19 is not tightly associated with any of the snRNAs required for the splicing reaction. No non-snRNP protein factor has been demonstrated to participate in either step of the spliceosome assembly pathway that PRP19 might be involved in. Thus, PRP19 represents a novel splicing factor.

Antibodies, Monoclonal↗
PubMed1992

A study of tobacco carcinogenesis. XLVII. Bioassays of vinylpyridines for genotoxicity and for tumorigenicity in A/J mice.

3-Vinylpyridine is formed from nicotine during the smoking of tobacco products. Consequently it is found in mainstream and side-stream smoke of cigarettes and cigars and in environmental tobacco smoke. In this study, 3-vinylpyridine and its isomers 2- and 4-vinylpyridine as well as styrene (vinylbenzene) were bioassayed for mutagenicity in Salmonella typhimurium strains TA 1535, TA 1538, TA 98 and TA 100 and for their genotoxicity in the rat hepatocyte DNA-repair test. In both in vitro assays-all three vinylpyridines and styrene were inactive. In a test for tumorigenicity in which the test compounds were injected intraperitoneally into A/J mice (total dose 200 mumol/animal) there was no significant incidence of lung adenoma nor of any other type of tumors.

Animals↗
PubMed1992

Lymphocyte subsets in healthy children during the first 5 years of life.

OBJECTIVE: To assess whether relative and absolute values of CD4 and CD8 lymphocytes and CD4/CD8 ratio change in relation to age, and to estimate the fifth and 95th percentiles for these values in children of various ages. PATIENTS AND METHODS: Phenotypic analysis of lymphocyte subsets was performed on blood samples from 208 healthy children, aged 1 through 59 months, using standard flow cytometric techniques. RESULTS: Regression analysis demonstrated that CD4 and CD8 lymphocyte counts declined significantly with advancing age (P less than .000001 and P = .03, respectively). Since CD4 and CD8 counts depend on total lymphocyte count, the percentage of total lymphocytes of each phenotype was also analyzed and demonstrated that the CD4 percentage was highly age dependent (P less than .000001). The CD8 percentage increased with age (P = .0001) but not as much as the CD4 percentage decreased. Median CD4 counts (fifth and 95th percentiles) for children 2 through 3, 4 through 8, 12 through 23, and 24 through 59 months of age were 2.83 (1.46 to 5.11), 2.95 (1.69 to 4.61), 2.07 (1.02 to 3.60), and 1.80 (0.90 to 2.86) x 10(9)/L, respectively. CONCLUSION: Healthy children's CD4 lymphocyte counts are considerably higher than previously established adult values. These data demonstrate that age is an important consideration in interpretation of lymphocyte subsets in children. This may be especially relevant in children who are infected with the human immunodeficiency virus, where CD4 lymphocyte values play a central role in monitoring disease progression and determining thresholds for medical interventions.

CD4-CD8 Ratio↗
PubMed1992

[Synthesis and antitumor activity of beta-germanyl-alpha-amino acid derivatives].

Some beta-germanyl-alpha-amino acid derivatives were prepared from the reaction of HGeCl3 with substituted oxazolines. The compositions of the above compounds were studied using IR, element analysis and so on. Experimental results were as follows: for 1-substituted-2-amino-2-carboxyethylgermanium susquioxide (such as IIIb), the po LD50 for mice was found to be above 10 g/kg. When given ip, a maximum inhibition of 50% of the growth of S180 was obtained for IIIb, whereas an inhibition of 42% was achieved for 5-Fu under the same experimental condition.

Amino Acids↗
PubMed1991

Absolute configuration of 7,12-dimethylbenz[a]anthracene-DNA adducts in mouse epidermis.

32P-Postlabeling was used to monitor the formation of DMBA-DNA adducts in mouse epidermis from each enantiomer of the trans 3,4-dihydrodiol. It was shown that the (4R,3R)-dihydrodiol is converted to the anti (4R,3S)-dihydrodiol (2S,1R)-epoxide which reacts with deoxyguanosine and deoxyadenosine residues in epidermal DNA to yield two of the major adducts formed when DMBA itself binds to epidermal DNA. The third major DMBA-derived adduct with deoxyadenosine residues was shown to arise from the (4S,3R)-dihydrodiol through the intermediacy of the syn (4S,3R)-dihydrodiol (2S,1R)-epoxide.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1991

The reproducibility of measuring the anorectal angle in defecography.

Dynamic proctography is a radiographic procedure that has become widely used in the evaluation of pelvic floor function. The anorectal angle (ARA) is one parameter which is usually quantified during this examination. To determine the accuracy with which this measurement can be made, three physicians independently measured the resting and squeezing ARAs of 22 women. The coefficient of variation and the kappa statistic were used to describe the degree of agreement among the three examiners. These analyses revealed poor agreement among examiners for all 22 patients taken as individuals, (kappa less than or equal to 0.40; mean coefficient of variation at rest = 18 percent; mean coefficient during squeezing = 21 percent). These results suggest that measurements of ARAs will vary among examiners for any particular patient, even though individual examiners may demonstrate consistency in recording ARA data. There is wide interobserver variation in the measurement of the ARA from lateral radiographs, making quantification an exercise of only limited clinical value.

Adult↗
PubMed1991

The spliced leader gene of Angiostrongylus cantonensis.

A 5' leader sequence has been identified on mRNAs of the parasitic nematode Angiostrongylus cantonensis. A 720-bp XhoI restriction fragment containing the gene encoding the leader sequence has been cloned and sequenced. It contains a 22-nt sequence identical to that of the leader sequence of Caenorhabditis elegans, a consensus splice site and a putative Sm antigen binding site. The gene is present as a tandem repeating unit of approximately 60 copies, and unlike C. elegans it is not associated with the 5S ribosomal RNA gene. The SL-RNA is 110 nt long and the sequence and primer extension studies suggest that it is transcribed from the tandemly repeating SL gene. It is precipitable from cell-free extracts of adult nematodes by anti-Sm anti-sera, and from RNA by anti-TMG anti-sera, thus suggesting its inclusion with small nuclear ribonucleoproteins in RNA splicing.

Amino Acid Sequence↗
PubMed1991

Electrical stimulation treatment of dog's denervated orbicularis oculi muscle.

In this investigation, the electrophysiology and pathology of denervated orbicularis oculi muscles have been studied in dogs during chronic electrical stimulation. The orbicularis oculi muscles were unilaterally denervated in 8 dogs, and 4 of these muscles were directly stimulated on a daily basis for 75 days. No difference in minimum stimulus intensities evoking orbicularis oculi muscle twitch contraction appeared between denervated treated and nontreated muscles. A significant reduction of minimum stimulus intensities evoking upper eyelid complete closure (blink), however, was found in the denervated treated muscles between 10 and 30 days (p less than 0.01). At 28 and 75 days, orbicularis oculi muscle biopsies showed no difference in muscle fiber diameter between denervated treated and nontreated muscles. At 75 days, type II muscle fiber distribution, however, was significantly increased in denervated treated muscles compared with denervated nontreated muscles (p less than 0.01). These findings of orbicularis oculi muscle electrophysiology were consistent with a transient reversal of denervation changes by electrical stimulation, partially supported by muscle biopsies.

Animals↗