BACKGROUND AND PURPOSE:One of the dilemmas facing clinicians treating patients with thyroid cancer is the evaluation of postthyroidectomy patients with rising serum thyroglobulin levels and indeterminate or normal findings on neck sonography. In this study, we examine the role of MR imaging in this subgroup of patients.
A vaccinia-directed deoxyribonucleic acid (DNA) polymerase has been partially purified from the cytoplasmic fractions of virus-infected HeLa cells. The utilization of natural and synthetic templates by this enzyme resembles that of the host cell DNA-dependent DNA polymerases. The vaccinia DNA polymerase cannot copy ribopolymers or ribonucleic acid but is very effective with an "activated" DNA as template. An exonuclease preferring single-stranded DNA as substrate is found in the most highly purified preparations of the enzyme. The molecular weight of the vaccinia DNA polymerase seems to be about 110,000. The viral DNA polymerase is also found to be associated with purified, infected cell nuclei, and this association may be due, at least in part, to nonspecific adsorption of the vaccinia DNA polymerase by nuclei. MATERIALS AND METHODS Cells, virus, and infection of cells. HeLa S-3 cells were grown in suspension cultures at 37 C in F-13 medium (Gibco, Grand Island, N.Y.) supplemented with 5%/ heat-inactivated fetal calf serum (Gibco) and 1%o lactalbumin hydrolysate (Gibco). Cells were harvested at 5 X 105 per ml, washed with 0.001 M KPO4 (pH 7.3) containing 0.32 M sucrose and 0.002 M MgCl2, and stored in liquid N2. For virus infection, cells grown to 5 X 105 per ml were collected by centrifugation and resuspended at 5 X 106 per ml in supplemented F-13 media with MgCl2 added to a final concentration of 0.02 M. Vaccinia virus, strain WR, was added at 2.5 to 3.5 plaque-forming units per cell, and the virus was allowed to adsorb for 1 hr at 37 C. The cells were diluted to 5 X 105 per ml with supplemented F-13 medium, incubated at 37 C for 6 hr, harvested, washed with 0.001 M KPO4 (pH 7.3)
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