Search PubMed⌕ Search

Biomedical subjects

C C Pao

Publications and source records attributed to C C Pao.

83 records · Page 5Linked to original sources
PubMed1979

A new nucleotide involved in the stringent response in Escherichia coli. Guanosine 5'-diphosphate-3'-monophosphate.

A novel nucleotide has been detected in Escherichia coli subjected to the stringent response. However, this nucleotide does not accumulate in relA+ cells subjected to heat shock, in which guanosine 5'-diphosphate-3'-diphosphate does accumulate but stable RNA synthesis is not restricted. The intracellular level of this new nucleotide thus correlates well with control of stable RNA synthesis. Chemical and enzymatic analysis shows that the new nucleotide is guanosine 5'-diphosphate-3'-monophosphate. It is suggested that this nucleotide may play a role in stringent control of stable RNA synthesis.

Escherichia coli↗
PubMed1978

A gene involved in the metabolic control of ppGpp synthesis.

A genetic locus has been identified which controls the basal synthesis of ppGpp in growing E. coli. Cells carrying a recessive allele of the relX gene have a very low concentration of ppGpp during balanced growth, and fail to accumulate ppGpp in response to carbon/energy source downshift. Moreover, the recessive relX allele renders the cells unable to grow at 42 degrees C and, when coupled with relA, makes the cells sensitive to the presence of leucine in minimal medium. RelX is cotransduced with fuc and relA and located at approximately 59.4 min on the E. coli genetic map.

Escherichia coli↗
PubMed1977

Anomalous synthesis of ppGpp in growing cells.

In E. coli cells, accumulation of ppGpp is normally triggered by conditions that restrict the aminoacylation of tRNA or interfere with carbon/energy source metabolism; in both cases, the nucleotide's accumulation is associated with control of stable RNA synthesis and is generally believed to bring it about. We have found an anomalous situation wherein vigorously growing cells accumulate a high level of ppGpp and there is no restriction of stable RNA synthesis. This occurs when wild-type cells are shifted up from an abnormally low growth temperature to one in the optimal range (35 degrees C-40 degrees C). The effect is partly, but not entirely, dependent upon the presence of a functional relA gene product. These results appear to call into question the simpler interpretations of the role of ppGpp in the control of stable RNA synthesis.

Amino Acids↗
PubMed1975

Mutants of T7 bacteriophage inhibited by lambda prophage.

Mutants in gene 20, a new T7 gene, cannot grow on rex+ lambda lysogens. Gene 20-- mutants suppress in double mutants the phenotype of T7 ligase negative mutations, but not vice versa. Amber 20- mutants have been obtained. There are differences between these T7 mutations and the similar T4 rII mutations. There are host mutations which permit T7 20- mutants to grow on lambda+ lysogens. T7 DNA synthesis on normal lambda+ lysogens infected with 20- mutants is essentially normal, but the DNA is not packaged. The gene 20 protein is active in in vitro complementation and probably used late in infection for DNA packaging into phage heads.

Chromosome Mapping↗
PubMed1973

Order of injection of T7 bacteriophage DNA.

The deoxyribonucleic acid (DNA) corresponding to the left-hand end of the genetic map is injected first in T7 phage infection. The order was deduced by use of marker rescue experiments to see which genes are still injected after the double-stranded DNA chain is broken by X rays. The treatment causes a selective loss of genes located on the right side of the map. Presumably, this corresponds to the tail end of normally injected DNA, and X rays cut off this end.

Chromosome Mapping↗
PubMed1971

[Diphtheria toxin].

Explore the source record for details and available documents.

Cell-Free System↗
PubMedDate not supplied

Changes of serum hepatitis B virus DNA in two types of clinical events preceding spontaneous hepatitis B e antigen seroconversion in chronic type B hepatitis.

Two types of clinical events, acute exacerbation and uneventful course, precede spontaneous HBeAg seroconversion to its antibody (anti-HBe) in chronic type B hepatitis. To examine the possible mechanism responsible for these two types of clinical events, serial serum specimens from 75 patients who underwent spontaneous HBeAg seroconversion were assayed for hepatitis B virus DNA by slot blot hybridization with 32P-labeled cloned hepatitis B virus DNA as probe. Of these 75 patients, 47 (62.7%) had episodes of acute exacerbation (ALT greater than 300 IU per liter) within 3 months prior to HBeAg seroconversion. All of these 47 patients had high hepatitis B virus DNA levels (greater than 1,000 pg per ml) at the onset of acute exacerbation. Their serum hepatitis B virus DNA disappears shortly before or simultaneously with the HBeAg clearance in 27 patients (57.4%) and persisted but with decreasing levels for 2 to 40 months in 20 patients. Most of these patients had high alpha-fetoprotein levels or evidence of bridging hepatic necrosis. In contrast, the serum hepatitis B virus DNA was undetectable for a minimum of 3 (3-17) months in the 28 patients who had an uneventful course before HBeAg seroconversion. Twenty of these 28 patients had well-documented episodes of acute exacerbation with high hepatitis B virus DNA levels, but with normal alpha-fetoprotein and little evidence of extensive necrosis as far back as 6 to 27 months before HBeAg seroconversion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

Acute exacerbation in chronic type B hepatitis: comparison between HBeAg and antibody-positive patients.

The incidence, clinicopathological features and etiology of acute exacerbation occurring in patients with chronic type B hepatitis were assessed prospectively among 385 patients who had HBeAg and 279 who had anti-HBe in serum. During an average follow-up of 23.5 months, acute exacerbations occurred in 197 HBeAg-positive patients and in 56 anti-HBe positive patients, with a calculated annual incidence of 28.6 and 10.3%, respectively (p less than 0.001). The clinical and laboratory findings of acute exacerbations were similar in the HBeAg-positive and anti-HBe positive patients. The mean serum bilirubin and alpha-fetoprotein levels were higher in anti-HBe positive patients (p less than 0.01), but actual differences were small. The histologic features of acute exacerbations were also similar in the HBeAg-positive patients and anti-HBe positive patients. Lobular alterations were the main histologic findings; in addition, one-fourth of patients had bridging necrosis and one-fourth had piecemeal necrosis. Spontaneous reactivation of hepatitis B was the major cause of these exacerbations in both HBeAg-positive patients (91.5%) as well as anti-HBe positive patients (62.5%). Hepatitis delta virus superinfection accounted for a higher percentage of exacerbations in anti-HBe positive patients (14.3%) than in HBeAg-positive cases (6.5%). Hepatitis A and possibly non-A, non-B virus superinfections also contributed to some episodes of exacerbation. Thus, acute exacerbations of disease occurred more frequently in HBeAg-positive patients than in anti-HBe positive patients with chronic type B hepatitis, but the clinicopathological features and etiologies were similar.

Acute Disease↗
PubMedDate not supplied

Loop conization for the treatment of microinvasive carcinoma of the cervix.

The purpose of the study was to evaluate the specimen adequacy and diagnostic accuracy of loop conization in microinvasive carcinoma of the cervix. A retrospective study was conducted from 1997 to 2003 at the Colposcopic Clinic, Department of Gynecology and Obstetrics, Chang Gung Memorial Hospital, Taipei, Taiwan. Sixty-three consecutive patients with microinvasive carcinoma of the cervix receiving cold-knife conization (35 patients) or loop conization (28 patients) were included in the study. All patients underwent definitive hysterectomy. We reviewed the conization specimen together with the hysterectomied uterus to compare the two conization techniques with respect to the histopathologic interpretation and diagnostic accuracy. The mean depth of cone specimens was significantly less in the loop conization compared with cold-knife conization (1.65 versus 2.35 cm, P = 0.035). Regarding the application of conization, the loop conization was completed in a single slice in 27 patients (77.1%) and in multiple slices in 8 patients (22.9 %), in spite of encouragement to perform conization in a one-pass application when possible. However, the cold-knife specimens were invariably a single cone-shaped piece. As reviewed by microscopic examination, the rate of tissue transection was significantly higher in the loop group than in the cold-knife group (14.3% versus 0%, P = 0.04). Because of tissue transection and disorientation, pathologic evaluation of stromal status was inadequate in 11.4% (4/35) of the loop cones as opposed to none of the 28 cold-knife cones. After assessing the hysterectomy specimens, the clinical diagnoses in the loop group were downgraded in three patients compared with only one in the cold-knife group. Data from this investigation suggest that cervical cold-knife conization is superior to loop conization as a method to assess microinvasive cervical cancer.

Adolescent↗