EFFECT OF 5-BROMODEOXYURIDINE AND ACTINOMYCIN D ON THE GROWTH OF VISNA VIRUS IN CELL CULTURES

Characterization of ribonucleic acid from visna virus

A single-stranded ribonucleic acid(s) has been isolated from purified virions of visna virus. It consists of two major components, namely 63S and "4S," under the conditions employed for ribonucleic acid (RNA) extraction. The 63S component can be converted to subunits by heat and dimethylsulfoxide treatments. Analyses by base composition indicate that the "4S" RNA isolated from visna virus is not a random breakdown product of the 63S component as a result of extraction, nor is it randomly derived from cellular RNA.

DNA polymerase activities in varions of visna virus, a causative agent of a "slow" neurological disease

The presence is reported of an RNA-instructed DNA polymerase in visna virus, the causative agent of a "slow" neurological disease in sheep. The product synthesized by the RNA-directed reaction has been shown to be a DNA heteropolymer by the following criteria: synthesis requires the presence of all four deoxyriboside triphosphates; the product is resistant to ribonuclease and alkali but is degraded by DNase; and the product has a density of 1.420 in Cs(2)SO(4) solution, characteristic of DNA.Visna virions, like those of the oncogenic RNA viruses, contain DNA polymerase activities that respond to a variety of double-stranded DNAs and to synthetic DNA.RNA hybrids.

Ribonucleic acid-dependent deoxyribonucleic acid polymerase in visna virus

A ribonucleic acid-dependent deoxyribonucleic acid polymerase was found in virions of visna virus. The enzyme product was resistant to ribonuclease and alkaline hydrolysis but susceptible to the digestion of deoxyribonuclease.

Transient inhibition of avian myeloblastosis virus reproduction by amethopterin and fluorodeoxyuridine

Avian myeloblastosis virus cannot initiate its reproduction in the presence of amethopterin or fluorodeoxyuridine. This inhibition is reversed by thymidine. Addition of either inhibitor after virus production has started does not inhibit further virus synthesis. In presence of either inhibitor, deoxyribonucleic acid synthesis is inhibited by over 90%, but ribonucleic acid synthesis is not affected. Cells resume their normal growth rate 24 hr after removal of either inhibitor.

The nucleic acid of African horse sickness virus

The effect of actinomycin D on the growth of African horse sickness virus in monkey kidney cells was studied. It was found that actinomycin D inhibited the yield of virus. It is suggested that African horse sickness virus is either a DNA containing virus or an RNA virus whose replication is DNA-dependent.