A mycovirus has been purified from mycelia of Penicillium chrysogenum by isopycnic centrifugation in sucrose and in CsCl. Viral particles band with a buoyant density of 1.20 in sucrose and 1.38 in CsCl. Particles have icosohedral symmetry, are 35 nm in diameter, and have an absorption profile characteristic of nucleoprotein. One enzymatic activity, RNA polymerase, is associated with the purified mycophage. Nucleic acid extracted from purified virus has a buoyant density in CS2SO4 of 1.61, a molar extinction coefficient of εp (258 nm) of 7200, a s20, w of 13.0, and a pattern of circular dichroism characteristic of double-helical ribonucleic acid. Molecules of this double-stranded ribonucleic acid (dsRNA), examined by electron microscopy, have a mean contour length of 0.86 μm which corresponds to a molecular weight of about 2.0 × 106 daltons. This dsRNA is resolved further by acrylamide gel electrophoresis into three closely spaced bands. Thermal denaturation of the viral dsRNA is dependent on ionic strength and gives a linear relationship with the negative logarithm of the sodium ion concentration.

sity in CS2SO4 as compared to RNA alone. Thermal melting studies show a marked increase in the Tm (ATm = 26°). Visible-region circular dichroic bands are induced when the dye is bound to RNA. These effects are also very similar to the results of studies on ethidium bromide-DNA complexes (Dalgleish, D. G.,

SynopsisThe ratio of the intrirlsic viscosities of the linear and circulitr forms of X DNA,

No abstract

Coxiella burnetii from acute cases of Q fever possess a plasmid termed QpH1. Chronic isolates contain a plasmid termed QpRS or have QpRS sequences integrated into the chromosome. The correlation between an isolate's plasmid type and the chronic or acute nature of the disease has prompted analysis of unique plasmid sequences to determine if they contain virulence genes. DNA hybridization has determined that a portion of a 3.6-kb EcoR I fragment (epsilon') is unique to QpRS. In vitro transcription/translation (IVTT) of the epsilon' fragment yielded a 55-kDa protein regardless of the cloning orientation, suggesting that transcription resulted from a rickettsial promoter. A translational start site was mapped to the 1.2-kb Pst I-EcoR I subfragment of epsilon' by IVTT. DNA sequencing showed an open reading frame (ORF) of 1485 bp, capable of coding for a protein of ca. 55.9 kDa. This ORF was termed cbbE'. Putative promoter regions of cbbE' included TTTAAT (-35), TATAAT (-10), and a ribosome-binding site GGAGAGA. The ORF ended with a stop codon UAA and was followed by UAG and a potential factor-independent transcription-termination region. In-frame cloning of the 695-bp Pst I subfragment into pUC9 resulted in a fusion protein of ca. 37 kDa, confirming the frame and length of the ORF as predicted by DNA sequencing. The specificity of this gene to QpRS was confirmed by probing DNA from three plasmid groups of C. burnetii, using the internal 695-bp Pst I fragment of cbbE'.