Correlation between replication and degradation of cellular DNA in polyoma virus-infected cells

Interactions of polyoma and mouse DNA's. II. Polyoma-induced mouse DNA replication and pseudovirion formation

Secondary mouse embryo (ME) cultures which had been grown prior to infection in the presence of 5-bromodeoxyuridine (BUdR) and 5-fluorodeoxy-uridine were found to be permissive for polyoma virus (16). The DNA extracted from the progeny virus yielded two bands on CsCl isopycnic centrifugation. The light band (LL) contained supercoiled circular (polyoma DNA I), open circular (polyoma DNA II), and linear (polyoma DNA III) molecules, as was seen by electron microscopy. The hybrid band (HL) contained exclusively linear molecules. This DNA was pure, density - labeled, pseudovirion DNA, i.e., fragmented HL mouse DNA. The quantitative comparison of HL and LL polyoma DNA III from six different virus preparations always revealed an excess of HL DNA, the ratio of HL/LL being between 1.2 and 2.2. These results led to the conclusion that in BUdR-prelabeled, polyoma-infected ME cells pseudovirion DNA is excised both from unreplicated and newly replicated regions of mouse DNA.

Viruses and evolution

This chapter discusses the role of viruses in nature. Viral transduction of structural and regulatory genes provides a means for information to leave the body of an organism other than through the germ cells. Natural selection acts upon the cell–virus nucleic acid coupling and the rate and direction of the evolution of any species depends upon the number of associated viruses and the extent to and speed with which they allow information to be cycled through the total gene pool of that population. There are three mechanisms by which gene material can be transferred from cell to cell: (1) transformation, (2) transduction, and (3) sexual conjugation. Transformation is the most random and inefficient process; it requires the laws of diffusion and the existing chemistry of the cell membrane, modified in contemporary cells by the development of transport systems, which facilitate membrane penetration. Transduction requires the development of genes for capsomere proteins to encapsidate nucleic acid and a sophistication of the process of membrane evagination to package nucleic acid into free particles, These are relatively modest genetic adaptations. However, true sexual union as it occurs in modern eukaryotes, requires such a high degree of cytological organization that it is inconceivable that it could have operated efficiently during the first billion or so years of cell evolution.

Breakdown of HeLa cell DNA mediated by vaccinia virus

Breakdown of HeLa cell DNA begins within 90 min after infection with vaccinia virus at a multiplicity of infection of 2-plaque-forming units per cell, and ends about 7.5 hr after infection. HeLa cell DNA is degraded to a uniform size of 1 to 2 x 10(7) daltons, as judged by alkaline sucrose sedimentation analysis. The rate of host-cell DNA degradation by vaccinia virus increased directly with the multiplicity of infection. Sedimentation patterns in neutral and alkaline sucrose gradients of viral DNA from infected cells, as well as from partially purified virions, indicated that two size classes of DNA were present. Class 1 DNA sediments like T4 DNA in neutral gradients and has a molecular weight twice that of T4 DNA in alkaline gradients. Class II DNA sediments as a molecule of lower molecular weight than T4 DNA in both types of gradients. Infection of prelabeled HeLa cells with vaccinia virus did not result either in formation of trichloroacetic acid-soluble radioactivity or, upon purification of the virions, radioactivity associated with class I DNA, indicating that vaccinia virus does not reutilize HeLa cell DNA.

Polyoma pseudovirions. II. Influence of host cell on pseudovirus production

The type of host cell influenced the relative amounts of pseudovirions and polyoma virions produced. The infection of primary mouse embryo cells resulted in the production of particles that were predominantly pseudovirions. Infection of baby mouse kidney or 3T3D cells yielded mainly infectious polyoma virus. The length of time that infection was allowed to continue also affected the amount of pseudovirions relative to polyoma virions. The longer the viral infection was allowed to proceed, the greater the quantity of pseudovirions produced. Pseudovirion production could be correlated with the fragmentation of host cell DNA to a size of approximately 3 x 10(6) daltons. The fragmentation of host cell DNA was much more extensive in primary mouse embryo cells than in the other cell types.

Relationship between replication of simian virus 40 DNA and specific events of the host cell cycle

The relationship between replication of simian virus 40 (SV40) DNA and the various periods of the host-cell cycle was investigated in synchronized CV(1) cells. Cells synchronized through a double excess thymidine procedure were infected with SV40 at the beginning or the middle of S, or in G(2). The first viral progeny DNA molecules were in all instances detected approximately 20 h after release from the thymidine block, independent of the time of infection. The length of the early, prereplicative phase of the virus growth cycle therefore depended upon the period of the cell cycle at which the cells were infected. Infection with SV40 was also performed on cells obtained in early G(1) through selective detachment of cells in metaphase. As long as the cells were in G(1) at the time of infection, the first viral progeny DNA molecules were detected during the S period immediately following, whereas if infection took place once the cells had entered S, no progeny DNA molecule could be detected until the S period of the next cell cycle. These results suggest that the infected cell has to pass through a critical stage situated in late G(1) or early S before SV40 DNA replication can eventually be initiated.

Polyoma pseudovirions. I. Sequence of events in primary mouse embryo cells leading to pseudovirus production

The relationship of the intracellular events leading to the production of polyoma pseudovirions in primary mouse embryo cells has been investigated. Replication of polyoma deoxyribonucleic acid (DNA) began 18 hr after infection. Assembly of viral capsid protein occurred 12 hr later. Intracellular fragments of host cell DNA, of the size found in pseudovirions, were first detected 36 hr after infection. The amount of intracellular 14S host DNA that was produced during infection was seven times greater than the amount of polyoma DNA synthesized. The relative pool sizes of polyoma DNA and 14S DNA at the time of virus assembly may dictate the amounts of polyoma virus and pseudovirus produced.

Multiplication of polyoma virus in mouse-hamster somatic hybrids: a hybrid cell line which produces viral particles containing predominantly host deoxyribonucleic acid

The multiplication of polyoma virus in a mouse-hamster (3T3 x BHK) somatic hybrid line (10A), which, although permissive for viral multiplication, produces very low amounts of virus, has been studied. In this cell line, the efficiency of productive infection is high, but the yield of infectious virus is on the order of 0.5% of that of 3T3 cells. The amount of viral deoxyribonucleic acid (DNA) synthesized by these cells upon infection is about 5% of that of 3T3 cells. An examination of the virus produced in hybrid 10A revealed that it was only one-tenth as infectious as the virus grown in 3T3. Although the viral DNA synthesized in the infected 10A cells is normal, the DNA extracted from purified virus grown in 10A consists of approximately 10% of normal, supercoiled polyoma DNA molecules and of approximately 90% linear DNA molecules with a sedimentation coefficient of 14 to 16S. These DNA molecules appear to be of cellular origin but contain a limited amount of viral DNA sequences. The host DNA-containing particles are not infectious but appear to possess some biological activity; they give rise to a weak complementation effect, and part of them are able to induce T-antigen synthesis. In addition, the host DNA present in these particles is predominantly that which has been synthesized after infection. The correlation between the block in viral DNA synthesis in this cell line and the abnormal encapsidation of host DNA is discussed.

Deoxyribonucleic acid replication in simian virus 40-infected cells. 3. Comparison of simian virus 40 lytic infection in three different monkey kidney cell lines

A comparative study of simian virus 40 (SV40) lytic infection in three different monkey cell lines is described. The results demonstrate that viral deoxyribonucleic acid (DNA) synthesis and infectious virus production begin some 10 to 20 hr earlier in CV-1 cells and primary African green monkey kidney (AGMK) cells than in BSC-1 cells. Induction of cellular DNA synthesis by SV40 was observed in CV-1 and AGMK cells but not with BSC-1 cells. Excision of large molecular weight cellular DNA to smaller fragments was easily detectable late in infection of AGMK cells. Little or no excision was observed at comparable times after infection of CV-1 and BSC-1 cells. The different kinds of responses of these three monkey cell lines during SV40 lytic infection suggest the involvement of cellular functions in the virus-directed induction of cellular DNA synthesis and the excision of this DNA from the genome.