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Y Hwang

Publications and source records attributed to Y Hwang.

10 recordsLinked to original sources
PubMed1996

Mutations affecting the high affinity ATPase center of gpA, the large subunit of bacteriophage lambda terminase, inactivate the endonuclease activity of terminase.

Phage lambda terminase carries out the cos cleavage reaction that generates mature chromosomes from immature concatemeric DNA. The ATP-stimulated endonuclease activity of terminase is located in gpA, the large terminase subunit. There is a high affinity ATPase center in gpA, and a match to the conserved P-loop of known ATPases is found starting near residue 490. Changing the conserved P-loop lysine at residue 497 of gpA affects the high affinity ATPase activity of terminase. In the present work, mutations causing the gpA changes K497A and K497D were found to be lethal, and phages carrying these mutations were defective in cos cleavage, in vivo. Purified K497A and K497D enzymes cleaved cos in vitro at rates reduced from the wild-type rate by factors of 1000 and 2000, respectively. The strong defects in cos cleavage are sufficient to explain the lethality of the K497A and K497D defects. In in vitro packaging studies using mature (cleaved) phage DNA, the K497A enzyme was indistinguishable from the wild-type enzyme, and the K497D enzyme showed a mild packaging defect under limiting terminase conditions. In a purified DNA packaging system, the wild-type and K497D enzymes showed similar packaging activities that were stimulated to half-maximal levels at about 3 microM ATP, indicating that the K497D change does not affect DNA translocation. In sum, the work indicates that the high affinity ATPase center of gpA is involved in stimulation of the endonuclease activity of terminase.

Adenosine Triphosphatases↗
PubMed1996

Kinetic and mutational dissection of the two ATPase activities of terminase, the DNA packaging enzyme of bacteriophage Chi.

Terminase the DNA packaging enzyme of bacteriophage chi, is a heteromultimer of gpNul (21 kDa) and gpA (74 kDa) subunits, encoded by the chi Nul and A genes, respectively. Sequence comparisons indicate that both gpNu1 and gpA have a match to the P-loop motif of ATPase centers, which is a glycine-rich segment followed by a lysine. By site-specific mutagenesis, we changed the lysines of the putative P-loops of gpNul (k35) and gpA (K497) to arginine, alanine, or aspartic acid, and studied the mutant enzymes by kinetic analysis and photochemical cross-linking with 8-azido-ATP. Both the gpNul and gpA subunits of wild-type terminase were covalently modified with 8-N3[32P] ATP in the presence of UV light. Saturation occurred with apparent dissociation constants of 508 and 3.5 microM for gpNul and gpA, resepctively. ATPase assays showed two activities: a low-affinity activity (Km=469 microM), and a high-affinity activity (Km=4.6 microM). The gpNul K35A and gpNul K35D mutant terminases showed decreased activity in the low-affinity ATPase activity. The reduced activities of these enzymes were recovered when 10 times more DNA was added, suggesting that the primary defect of the enzymes is alteration of the nonspecific, double-stranded DNA binding activity of terminase. ATPase assays and photolabeling of the gpA K497A and gpA K497D mutant terminases showed reduced affinity for ATP at the high-affinity site which was not restored by increased DNA. In summary, the results indicate the presence of a low-affinity, DNA-stimulated ATPase center in gpNul, and a high-affinity site in gpA.

Adenosine Triphosphatases↗
PubMed1995

A defined system for in vitro lambda DNA packaging.

We constructed a defined in vitro system for packaging lambda DNA which is composed of purified proheads, the noncapsid proteins terminase and gpFI, and the Escherichia coli DNA binding/bending protein IHF. The defined packaging system: (i) is free from endogenous ATP, DNAs, and DNases and (ii) packages 30% of the input mature lambda DNA efficiently. In this defined packaging system, IHF and gpFI make modest contributions to packaging efficiency. The defined packaging reactions showed that DNA packaging gave a linear response to the concentration of mature lambda DNA and terminase. DNA packaging showed a sigmoidal relationship with respect to the concentration of ATP and proheads.

Adenosine Triphosphate↗
PubMed1995

Physicians' response to length-of-stay profiling.

One of the techniques adopted recently by certain hospitals to meet the competitive pressure for reducing costs is physician profiling. Profiling produces periodic reports that compare a physician's resource consumption to a benchmark figure. This study analyzes the effectiveness and implications of one hospital's introduction of physician patient length-of-stay profiling. Data for 24,000 patients treated by 400 physicians in 450 diagnosis-related groups over 42 months were analyzed, including both preprofiling and postprofiling periods. Statistical tests examined whether more physicians achieved the length-of-stay benchmark after profiling was introduced, controlling for physician, disease category (diagnosis-related group), and patient severity level. First, the results establish a significant increase in the percentage of physicians who achieve the length-of-stay benchmark after the introduction of profiling. Second, it was found that physicians who had initially failed to meet the benchmark reduced their patients' average length of stay much more than those physicians who initially achieved the benchmark. Further, reductions occurred primarily at intermediate severity levels, and in diagnosis-related groups with a large economic impact for the hospital. Although the profiling program did achieve the objective of reducing patient length of stay, further improvement may be possible. First, providing different benchmarks or targets for different physicians may extend the improvement to a greater percentage of all physicians involved. Second, an analysis of monthly data on total weighted procedures reveals that the reduction in length of stay resulted in an increase in the number of procedures performed per patient day. This finding suggests that to achieve a reduction in hospital costs and charges, profiling programs should be combined with process improvement initiatives.

Diagnosis-Related Groups↗
PubMed1992

[The factors of diagnosis and treatment delay in the late stage of cancers in pharynx, larynx and oral cavity].

Cancers of pharynx, larynx and oral cavity (CPLOC) are the tumors can be easily found by patients themselves. Unfortunately, the diagnosis and treatment delay in CPLOC is very severe in our country. The study was based on the data collected through questionnaire from 100 patients with CPLOC in late stages. The causes of diagnosis and treatment delay in those patients were evaluated. The study reveals that traffic and financial difficulties are not the principal factors causing the delay. Instead, limited knowledge which the patients learned from television and newspapers, and sometimes bias cancer knowledge play major role in the delay. When the symptoms developed, 64% of the patients either did not pay attention to their symptoms, or took some improper medical treatments according to their own diagnosis. It took them 207 days on average from having the symptoms to consulting a doctor, about 108 days on average from consulting a doctor to getting a right suggestion. The latter delay was often caused by ambiguous and improper suggestion from doctors. However, if a patient receives a proper suggestion from a doctor, the major reason for diagnosis delay was that patients felt their symptoms were not severe or the examinations required too much time. Even if patients were confirmed to have cancer, treatment delay is still not avoidable as they often turned to Chinese herb doctors, took herb drugs, or feared of receiving an operation. Therefore, the best way of reducing treatment delay in CPLOC is to enhance medical knowledge and education, and to correct the image that traditional Chinese herbs are effective in curing CPLOC.

Adult↗
PubMed1991

Expression of penicillin G acylase gene from Bacillus megaterium ATCC 14945 in Escherichia coli and Bacillus subtilis.

Penicillin G acylase gene from Bacillus megaterium ATCC 14945 has been isolated. Recombinant Escherichia coli clones were screened for clear halo forming activity on the lawn of Staphylococcus aureus ATCC 6538P using the enzymatic acylating reaction of 7-aminodeacetoxycephalosporanic acid (7-ADCA) and D-(alpha)-phenylglycine methylester. The gene was contained within a 2.8 kb DNA fragment and expressed efficiently when transferred from E. coli to Bacillus subtilis. A twenty times greater amount of enzyme was produced in B. subtilis transformant than that in B. megaterium. The purified enzyme from subcloned B. subtilis showed that the native enzyme consisted of two identical subunits, each with a molecular weight of 57,000. The enzyme was able to react on various cephalosporins, i.e., cephalothin, cefamandole, cephaloridine, cephaloglycin, cephalexin and cephradine.

Bacillus megaterium↗