Search PubMed⌕ Search

Biomedical subjects

R C Yang

Publications and source records attributed to R C Yang.

72 records · Page 4Linked to original sources
PubMed1982

Use of annular artificial pupil in the determination of modulation transfer function of the eye.

According to Ref. [1] primary spherical aberration of the schematic eye would be completely absorbed by an annular aperture when its obstruction ratio epsilon is greater than or equal to 0.60. Consequently the contrast sensitivity function, Tcs, determined with the use of such an annulus, Tcs (A), is the MTF of the retina-brain system, Trb, weighted by the MTF of the annulus, T. . Trb thus obtained can be used to determine the MTF of the eye, Te. Annular apertures of various sizes and obstruction ratios used for the determination of Te have been analysed. It is shown that there are several factors other than incomplete absorption of primary spherical aberration that would prevent the use of annular pupil to derive Trb under unrestrained conditions. This is due to the fact that the apparent T.'s of annuli used in the actual determination of Tcs(A) usually deviate from the theoretical T.'s for the passive eye to different extents. However, it is found that the T. for annulus of o.d. = 2.7 mm and epsilon = 0.60 conforms more or less to the theoretical T. and can be used to derive reasonably accurate Te(2.7). It is also possible to estimate Te(less than 2.7) from Te(2.7) by some empirical correction.

Adaptation, Ocular↗
PubMed1980

Postoperative maxillary cyst.

The postoperative maxillary cyst develops in the maxillary sinus between the ages of 30 and 40 in persons who received sinus surgery 10 to 20 years earlier. Etiology of the cystic lesion appears to be derived from the infected sinus mucosa left after a sinus operation. Chief complaints of postoperative maxillary cysts are swelling or pain in the buccal region, discomfort of the maxilla or maxillary teeth and exophthalmos. Characteristic panoramic radiographic findings of the postoperative maxillary cyst are a monolocular cystic radiolucency with a well-defined margin and surrounding sclerotic bone in the floor of the maxillary sinus.

Adult↗
PubMed1980

BK virus DNA sequence coding for the t and T antigens and evaluation of methods for determining sequence homology.

The DNA sequence of the early region of the human papovavirus BK (MM strain) was determined. A potential initiation signal for translation is located at nucleotides 3,047 to 3,045 or map position 0.614. Extending counterclockwise from this AUG signal there is only one open reading frame, which can code for a putative t antigen of 100 amino acids in length. If the early mRNA of BKV is spliced, then the regions between nucleotides 3,047 to 2,808 and 2,725 to 884 can code for a T antigen 694 amino acids in length. The sequences of the deduced T antigens in BK virus share 71% amino acid homology with those in simian virus 40, whereas the coding sequences of the two viruses share 70% DNA homology. Comparison of DNA sequences and evaluation of homology measurements between these two viruses are discussed.

Antigens, Neoplasm↗
PubMed1979

BK virus DNA: complete nucleotide sequence of a human tumor virus.

The complete DNA sequence of the human papovavirus BK is presented. From the 4963 base-pair sequence of BK virus (MM strain), the amino acid sequence of at least five proteins can be deduced: a T antigen and a t antigen, which share amino terminal peptides; proteins VP2 and VP3, which share 232 amino acids; and protein VP1, whose coding sequence overlaps those for VP2 and VP3 by 113 nucleotides but is read in a different frame. The gene loci and the arrangement of genes are strikingly similar in BK virus and simian virus 40 (SV40). The sequence of the deduced proteins in BK virus shares 73 percent amino acid homology with those in SV40, whereas the DNA sequence of the two viruses shares 70 percent homology, suggesting close evolutionary relationship. However, the repeated DNA sequences in the noncoding regions of these viruses are different.

Antigens, Viral↗
PubMed1979

Comparative study of papovavirus DNA: BKV(MM), BKV(WT) and SV40.

Extensive physical mapping revealed that approximately 90% of the genomes of BKV(prototype, WT) and BKV (MM strain) are identical or closely related. Nucleotide sequences of the non-homologous regions and a large portion of the homologous regions have been determined for both genomes. The coding sequence of small t antigen of BKV(MM) is 216 nucleotides shorter than that of BKV(WT), even though no differences in biological function of the t antigen was observed. Both genomes contain three similar sets of 44-61 base-pair repeated sequences. However, the DNA sequence of the tandem repeats is totally different between BKV (human cell as host) and SV40 (monkey cell as host). On the other hand, the region between the N-terminus of the T antigen genes and the origin of replication is dominated by a similar set of palindromic sequences in BKV and SV40 DNA. There is also extensive homology between the regions which code for proteins in BKV and SV40, suggesting a close evolutionary relationship.

Antigens, Viral↗
PubMed1979

BK virus DNA sequence: extent of homology with simian virus 40 DNA.

The primary nucleotide sequence of three regions of BK virus (BKV) variant (MM) DNA has been determined. The region between map positions 0.715 and 0.900 includes the initiation points and partial coding sequences of the putative VP2 and VP3 proteins of BKV(MM), the amino acid sequences of which show over 80% homology with those of VP2 and VP3 of simian virus 40. The sequence of a potential leader protein X, 66 amino acids long for BKV(MM) and 62 long for simian virus 40, is also deduced. The regions between 0.595 and 0.398 and 0.310 and 0.175 include the coding sequence for the entire small t antigen and most of the large T antigen of BKV(MM). The DNA sequence within these regions comprises over 50% of the complete BKV(MM) genome and shows a 70% sequence homology with the corresponding regions of simian virus 40 DNA. This high degree of homology is at variance with the reported homology values of 11--20% estimated by hybridization measurements of heteroduplex analyses. Possible explanations for the discrepancy are discussed.

BK Virus↗
PubMed1978

BK virus DNA: cleavage map and sequence analysis.

A detailed physical map of the BK virus (MM strain) genome has been constructed with respect to the cleavage sites of 11 different restriction enzymes. The enzymes cut BKV(MM) DNA at 61 specific sites whose locations have been determined. Preliminary nucleotide sequence was carried out in the region from 0.70-0.75 map positions on BKV(MM) DNA. An 80% homology was found at 0.714-0.744 map positions on BKV(MM) DNA with 0.722-0.752 map positions on simian virus 40 DNA. This region of simian virus 40 DNA codes for the synthesis of the leader sequence of late mRNA.

Animals↗
PubMed1978

Cleavage map of BK virus DNA with restriction endonucleases MboI and HaeIII.

Specific cleavage of BK virus (MM) DNA with restriction endonuclease MboI gives rise to 10 fragments. Two techniques were used to determine the location of these fragments on the viral genome with respect to the three known sites for HindIII cleavage. In the first method, reciprocal digestion, individual MboI fragments were digested with HindIII and individual HindIII fragments were digested with MboI. In the second method, single-end 32P-labeled HindIII subfragments were partially digested with MboI, and then the sizes of the radioactive partial products were used to deduce the nearest neighboring fragment. Information from these two methods is more than adequate to map all the MboI enzyme sites. Cleavage of BK virus (MM) DNA with restriction enzyme HaeIII produces 21 fragments. With the aid of the same two methods, these fragments have also been ordered with respect to the known map locations of the HindIII and MboI sites.

BK Virus↗
PubMed1978

Physical mapping of BK virus DNA with SacI, MboII, and AluI restriction endonucleases.

A new restriction endonuclease, SacI from Streptomyces achromogenes cleaves BK virus (strain MM) DNA into 3 fragments, whereas MboII from Moraxella bovis and AluI from Arthrobacter luteus give 22 and 30 fragments, respectively. All these specific DNA fragments were ordered and mapped on the viral genome by two methods first, by the reciprocal digestion method using uniformly 32P-labeled DNA; and second, by the partial digestion technique using the single-end 32P-labeled DNA. This study, together with those reported earlier, defined the location of 90 cleavage sites on the BK virus DNA.

BK Virus↗
PubMed1978

Electro-acupuncture analgesia in monkeys: a behavioral and neurophysiological assessment.

Monkeys were initially trained to press a lever to escape noxious electrical stimulation applied to one leg. They were then presented with electrical stimuli consisting of 40 successive intensity increments beginning at zero intensity and with random interstimulus intervals (ISIs). A lever press, initiated by the monkey during presentation of a stimulus, immediately terminated stimulation of the leg, triggering another sequence of the same increasing stimuli with a new series of ISIs. After establishment of a stable threshold measure of lever pressing, 45 min of electro-acupuncture was applied to traditional points on both legs. The results show that electro-acupuncture dramatically increased (300-400 %) the lever pressing threshold for approximately 20 min after electro-acupuncture stimulation was terminated. In acute monkey preparations, spike activity of single neurons in N. Parafascicularis of the thalamus, evoked by noxious electrical stimulation to the sciatic nerve, was recorded. The evoked activity of only nociceptive specific neurons was either eliminated or markedly reduced for at least one hour following 45 min of electro-acupuncture applied to traditional points on both legs. The observations made by these two experimental approaches suggest that electro-acupuncture exerts an analgesic effect on artificially induced nociception.

Acupuncture Therapy↗
PubMed1976

Cleavage map of the simian-virus-40 genome by the restriction endonuclease III of Haemopholus aegyptius.

Enzymic digestion of Simian virus 40 (SV40) DNA with Haemophilus aegyptius restriction endonuclease Hae III results in 10 major and eight minor fragments. These were resolved by electrophoresis on graduated polyacrylamide slab gels. All fragments have been characterized with respect to the size relative to the Haemophilus influenzae Rd fragments (Hind). They were ordered on the SV40 DNA map by means of overlap analysis of the double cleavage products derived from sequential digestion of Hind fragments with Hae III endonuclease and Hae fragments with Hind II + III enzyme, as well as by other reciprocal cleavage experiments, including those involving Haemophilus para-influenzae fragments. In this way the 18 Hae III cleavage sites and the 13 Hind sites have been localized on the circular SV40 DNA map.

Base Sequence↗
PubMed1976

Specific cleavage and physical mapping of simian-virus-40 DNA by the restriction endonuclease of Arthrobacter luteus.

Simian virus 40 (SV40) DNA (strain 776) is cleaved by the restriction endonuclease from Arthrobacter luteus into 32 specific fragments including 20 large pieces designated Alu-A through T as well as 12 minor products named Alu m1 through m8. These were mapped on the SV40 genome by double digestion experiments. Alu fragments were treated with Hind enzymes and vice versa. Similar reciprocal digestions were also carried out with Hae III enzyme. In this way a detailed cleavage map of the SV40 genome could be constructed.

Arthrobacter↗
PubMedDate not supplied

RAPD variation within and among natural populations of trembling aspen (Populus tremuloides Michx.) from Alberta.

This article described the population structure of trembling aspen (Populus tremuloides Michx.) in Alberta, a dioecious tree with continuous and wide distribution, and with a primary mode of reproduction through suckering. We studied random amplified polymorphic DNA (RAPD) variation in 249 trees from eight natural populations. Trees within a population were a minimum of 200 m apart to decrease the risk of sampling ramets of a single ortet. Of a total of 28 amplified RAPD products (bands) from five random oligonucleotide primers, the frequencies at seven (25%) were heterogeneous across populations and the percentage of polymorphism averaged 90.2 per population. Estimates of Shannon's phenotypic diversity index ranged between 0.58 and 0.69 among populations, averaging 0.65. There were 246 multiband phenotypes among the 249 trees; three were each shared by two trees from different populations and the remaining 243 were unique. Thus, trees within populations probably were different clones. Analysis of molecular variance partitioned the RAPD variation into the among- and within-population components. The within-population component accounted for 97.4% of the variation and was significantly different from zero at the 2% level of probability. The among-population component, although accounting for only 2.6% of the variation, was significantly different from zero at the 1% level of probability. Pairwise tests for the homogeneity of the RAPD variance between populations suggested significant divergences among 18 of the 28 (64%) population pairs.

Alberta↗