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Biomedical subjects

W C Summers

Publications and source records attributed to W C Summers.

At least 73 records · Page 4Linked to original sources
PubMed1978

Characterization of the mRNA for herpes simplex virus thymidine kinase by cell-free synthesis of active enzyme.

The cytoplasmic mRNA which codes for the herpes simplex virus specific thymidine kinase (TK) is polyadenylated and is 14.5s in size. This corresponds to an RNA of 1400 nucleotides. The TK polypeptide is about 42,000 daltons, which requires 1100 nucleotide. We conclude that the cytoplasmic mRNA is monocistronic. The reticulocyte lysate cell-free translation system synthesizes enzymatically active HSV-TK which can be assayed with high specificity and sensitivity by use of 125I-iododeoxycytidine as a substrate.

Cell-Free System↗
PubMed1978

Structure of the joint region and the termini of the DNA of herpes simplex virus type 1.

Analysis of restriction endonuclease cleavage sites within the inverted, repeated sequences in the joint region of the DNA of herpes simplex virus type 1 strain KOS revealed the presence of two types of sequence heterogeneity. The first was an insertion of 280 base pairs or multiples of 280 base pairs which was found in approximately half of all DNA molecules from every plaque-purified stock of virus. These insertions seemed to be tandem duplications of sequences which were present at the joint and correspond closely to the inverted terminal redunancy. The second type of heterogeneity was due to variable insertions and deletions which were present in some, but not all, plaque-purified virus stocks. Comparison of restriction fragments from the joint region with fragments from the termini indicated that in the simplest observed molecules of herpes simplex virus type 1 DNA, only one copy of the inverted terminal redundancy was present at the joint. A map of restriction endonuclease cleavage sites in the joint region is presented.

Base Sequence↗
PubMed1978

The thymidine kinase gene of herpes simplex virus type 1: cell-free protein synthesis and substrate specificity studies.

The HSV thymidine kinase genetic system has a number of advantages for the study of virus and cell genetics. Both forward and reverse mutants are readily selected. The enzyme can be assayed directly in the presence of the cell TK by the choice of the appropriate substrate, for example, 125IdC. The gene product, HSV TK, can be identified by SDS-polyacrylamide gel electrophoresis and mutants can be found with alterations in the electrophoretogram. The in vitro synthesis of HSV TK in response to HSV mRNA has been achieved and can be used to analyse specific mutant virus.

Cell-Free System↗
PubMed1977

Cell-free synthesis of herpes simplex virus proteins.

Polyribosomes isolated from herpes simplex virus type I (HSV-1)-infected cells have been used to program a eucaryotic cell-free translation system. At least 10 HSV-specific polypeptides, with apparent molecular weights of 25,000 to 160,000, are synthesized by wild-type HSV-infected polyribosomes. Polyribosomes prepared from thymidine kinase-negative mutants of HSV direct the synthesis of three putative nonsense termination polypeptides. HSV-specific polypeptides synthesized in vitro are precipitated with antiserum to HSV-infected cell proteins.

Animals↗
PubMed1977

[125I]deoxycytidine used in a rapid, sensitive, and specific assay for herpes simplex virus type 1 thymidine kinase.

[125I]deoxycytidine was a good substrate for herpes simplex virus type 1 thymidine kinase (TK), whereas [125I]deoxycytidine was a very poor substrate for cellular TK. Simple, sensitive, and specific assays for viral TK could be carried out in vivo and in vitro even in the presence of cell TK. Autoradiographic detection of incorporated [125I]deoxycytidine provided a rapid and simple method for detection of and screening for viral TK in infected as well as viral TK-transformed cells.

Cell Line↗
PubMed1976

Inhibition of Epstein-Barr virus DNA synthesis and late gene expression by phosphonoacetic acid.

Growth of lymphoblastoid cells (B95-8, Raji) is not inhibited by the presence of 0.4 mM phosphonoacetic acid. The synthesis of Epstein-Barr virus (EBV) in the producer line B95-8 is completely inhibited, as shown by the total inhibition of viral capsid antigen synthesis. Early viral antigens are made normally in the presence of phosphonoacetic acid, but EBV DNA synthesis is blocked in cells entering the productive cycle. Nonproducer cells in the population replicate the resident EBV DNA by a mechanism that is resistant to phosphonoacetic acid. These results are consistant with the hypotheses that EBV DNA is replicated by two mechanisms, one in the noninduced cell and a different mechanism in the producer cell, and that prior replication of EBV DNA, probably by the second mode, is a prerequisite for late gene expression.

Acetates↗
PubMed1976

Nucleic acid renaturation and restriction endonuclease cleavage analyses show that the DNAs of a transforming and a nontransforming strain of Epstein-Barr virus share approximately 90% of their nucleotide sequences.

Viral DNA molecules were purified from a nontransforming and a transforming strain of Epstein-Barr virus. Each viral DNA was labeled in vitro and renatured in the presence of an excess of either one or the other unlabeled viral DNA. Both viral DNAs were also digested with the Eco R1 restriction endonuclease and subsequently labeled by using avian myeloblastosis virus DNA polymerase to repair either the EcoR1 nuclease-generated single-stranded ends of the DNAs or their single-stranded ends produced by a second digestion with exonuclease III after the first EcoR1 nuclease digestion. The results of these experiments support three general conclusions: (i) the DNAs of these two strains of Epstein-Barr virus share approximately 90% of their nucleotide sequences; (ii) both viral DNA populations are reasonably homogenous; and (iii) both DNAs contain repetitions or inverted repetitions of some of their nucleotide sequences.

Base Sequence↗
PubMed1976

Head and neck cooling by air, water, or air plus water in hyperthermia.

The effects of air, water, and air plus water head cooling on thermoregulatory responses and human operator performance were studied in nonacclimatized, heat-exposed men. Forty chamber exposures (46 degrees C, 30 mm Hg water vapor pressure) were conducted under noncooled and the aforementioned subconditions of head cooling. Five subjects, exposed for 80 min, were monitored for mean skin and rectal temperatures, heart rate, sweat loss, and compensatory tracking performance. A modified Air Force helmet shell provided facial air ventilation (24 degrees C) at 8 cfm. Eight interconnected neoprene modules fastened beneath a helmet linear provided water cooling (20 degrees C at 0.9 l/min). Tracking performances was unchanged across conditions. Elevation of rectal temperature and heart rate, sweat loss, and Physiological Index of Strain were significantly reduced by each condition of head cooling. Air is as effective as water as a cooling agent. Air ventilation acts synergistically with water cooling in reducing physiological strain. Relative merits of each approach to head cooling, in an operational context, are discussed.

Adult↗
PubMed1975

Possible peptide chain termination mutants in thymide kinase gene of a mammalian virus, herpes simplex virus.

Mutations in the viral gene coding for the thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.75) induced by herpes simplex virus have been obtained by selection of virus resistant to bromodeoxyuridine when grown in thymidine-kinase-deficient LMTK- mouse cells. Proteins labeled after infection of Vero (monkey) cells with herpes simplex virus were analyzed by gel electrophoresis and one protein of about 40,000 daltons was consistently altered in a number of thymidine-kinase-deficient mutants. Many viral mutants lacked this peptide and one class of these mutants induced the synthesis of new shorter peptides. Revertant virus could be selected which simultaneously regained the ability to induce thymidine kinase activity, regained the intact thymidine kinase peptide, and lost the ability to synthesize the shorter peptide fragment. These mutants comprise a class of animal virus mutants which have the properties expected of peptide chain termination mutants.

Bromodeoxyuridine↗
PubMed1975

Structure and function of herpesvirus genomes. I. comparison of five HSV-1 and two HSV-2 strains by cleavage their DNA with eco R I restriction endonuclease.

The restriction endonuclease Eco R I cleaves HSV-1 and HSV-2 DNA into specific fragments that can be resolved by agarose gel electrophoresis. Comparison of HSV-1 strains KOS, 14-012, MP, F, and CI 101, and HSV-2 strains 333 and 186, suggests that the DNAs from type 1 strains are similar but not identical, and that the type 2 strains differ greatly from type 1 strains. The molecular lengths of the fragments have been determined by electron microscopy and can be used to calibrate gel electrophoretic analyses of DNA fragments.

Agar↗