Crystallization of cauliflower mosaic virus

Cauliflower mosaic virus has been crystallized in hanging and sitting drops. The hexagonal and octahedrally shaped crystals are up to 0.5 mm in mean diameter. The octahedrally shaped crystals diffract to about 27 A resolution. The results are discussed in relation to the lability and aggregation of the virions.     

Phosphorylated proteins in cauliflower mosaic virus

Autoradiography of dodecyl sulfate-impregnated polyacrylamide gels after electrophoresis of the proteins from 32P-labeled cauliflower mosaic virus (CaMV) showed that two of the structural proteins were phosphorylated. These two proteins of 44 and 58 kilodaltons (kd) occur as minor components with some strains of the virus, but with other virus strains under particular conditions the 44-kd protein appears as a major component of the virion. The site of phosphorylation was found to be phosphoserine and phosphothreonine. It is suggested from these results that the 58-kd protein may be the primary translation product of the coat protein gene of CaMV and that the 44-kd and other lower molecular weight forms of the coat protein are derived from this polypeptide by proteolysis.     

Host range control of cauliflower mosaic virus

Studies with recombinant genomes of cauliflower mosaic virus (CaMV) strains D4, CM1841, and Cabb-B have shown that a host range determinant of CaMV is encoded within the first half of region VI, a gene which codes for P62, an inclusion body protein. In order to further study the host specificity of CaMV, a fourth CaMV strain, W260, was chosen that has a host range that is intermediate between D4 and CM1841. To determine which portion of the W260 genome controls systemic spread, recombinant viruses made between this strain and CM1841 and D4 were tested for their ability to systemically infect several solanaceous plants (Datura stramonium, Nicotiana edwardsonii, and Nicotiana bigelovii). The first half of gene VI specified the type of local lesions and systemic spread of recombinant strains in D. stramonium. In N. edwardsonii, it was found that the first half of gene VI controlled the type of local lesion formed but systemic spread was dependent on the whole of gene VI. In N. bigelovii the number of genes that determined systemic spread of CaMV varied with the strain of CaMV. Systemic spread of D4 in N. bigelovii was dependent on the first half of gene VI. In contrast, systemic spread of W260 in the same host was dependent on the whole of gene VI and another locus which mapped within genes I-V. Consequently, it appears that other viral proteins may interact with P62 or that P62 may function well in some hosts only in compatible forms of other viral proteins.     

The structure of cauliflower mosaic virus genome

Native cauliflower mosaic virus (CaMV) DNA sedimented as two major components, a nicked circular form (19.0 S) and a linear form (17.1 S). Upon electrophoresis in 2.5% polyacrylamide gels the nicked circular form migrated more slowly than the linear form. The nicked circular form was infectious; the linear form had little infectivity. Upon denaturation using heat and formaldehyde or alkali treatment for a short time, CaMV DNA sedimented as two components (16.1 S and 13.5 S) in sucrose density gradients. These were considered to be the single-stranded circular and linear forms respectively. After prolonged alkali treatment some of the CaMV DNA broke down into fragments with an average size of one-quarter to one-fifth of the normal single-stranded length. The nature of the alkali-labile regions was investigated and ribonucleosides, comprising less than 1% of the total nucleic acid, were identified. The significance of these findings is discussed.     

A procedure for rapid isolation and analysis of cauliflower mosaic virus DNA

A simple and rapid procedure has been developed for the small-scale isolation of crude preparations of cauliflower mosaic virus DNA. The preparations are relatively free of contaminating cellular DNA and are sufficiently pure to be digested with restriction enzymes. The method enables plants infected with single-lesion isolates of mutagenized viral DNA to be rapidly screened for particular restriction endonuclease sites.     

Glycosylation of the cauliflower mosaic virus capsid polypeptide

Evidence is presented for the glycosylation of the cauliflower mosaic virus (CaMV) capsid polypeptide. Fluorescent derivatives of concanavalin A (Con A) were shown to bind specifically to the dissociated CaMV capsid polypeptides in polyacrylamide gels. Con A also bound specifically to intact CaMV, so inhibiting the attachment of virus-specific antibodies. The role of carbohydrate residues in CaMV antigenicity is evaluated.     

The coat proteins of cauliflower mosaic virus.

Four polypeptides with molecular weights and molar ratios (in parentheses) of 96,000 and 88,000 (both 0.08), 64,000 (0.15) and 37,000 (0.77) were found in purified preparations of cauliflower mosaic virus (CaMV). Two further polypeptides were found in some preparations and one was shown to be a degradation product of the major polypeptide. The four proteins found consistently had uniform charge/size ratio and gave positive but faint reaction to periodate-Schiff stain for glycoprotein. It is proposed that CaMV particles are composed of a T = 7 shell of the major protein surrounding a T = 1 core of the 64,000 molecular weight protein.     

Free cauliflower mosaic virus supercoiled DNA in infected plants

Evidence is presented indicating that free viral DNA exists in Cauliflower mosaic virus-infected leaves. Among the different viral DNA forms detected in total DNA extracts is a supercoiled form. We discuss its possible role in the replication process.     

Comparative cytology of nine isolates of cauliflower mosaic virus

The cytology of nine isolates of cauliflower mosaic virus was compared by light and electron microscopy. Differences noted among the isolates were: the size of cytoplasmic inclusion bodies, frequency of virions occurring free in the cytoplasm as opposed to those in inclusions, the ratio of virions to the amount of matrix protein in inclusions, and intraplastidial inclusions induced by one of the isolates. It was concluded that these four cytological features are expressions of the viral genome rather than the host. One of the isolates induced different sized inclusions in two different hosts.