Fine Structure of the Coat and Nucleoid Material of Fowlpox Virus

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Abstract
Several morphological forms characteristic of the poxvirus group were demonstrated for fowlpox virus with neutral phosphotungstic acid (PTA). Viral particles (purified from viral inclusion bodies) stained with uranyl acetate (UA) and shadowed with platinum were shown to have an external knobby surface not evident with PTA. The external coat of freshly purified viral particles seemed intact, but as the preparation aged, it appeared to unwind, resulting in twisted "rope-like" structures. This process was facilitated by use of 1% trypsin, and three dense fibrils were identified with UA within the partially detached viral coat. Studies with alkaline PTA (pH 9) were interpreted as revealing a complex nucleoid, but solutions above this pH damaged the particles. The morphology of the nucleoid was better depicted in ultrathin sections of whole virus which, when stained with UA, revealed dense coiled threads. Treatment of virus with sodium lauryl sulfate exposed an underlying coat consisting of small subunits approximately 40 A in diameter. Of great interest was the demonstration that the detergent removed strands of deoxy-ribonucleic acid (DNA) from the virus without destroying the contour of the particle. The origin of the strands was definitely the fine urano-philic, coiled threads of the nucleoid, which probably represent the DNA molecule (s). That the extracted material was largely DNA was proved by digestion with deoxyribonuclease and resistance to ribo-nuclease and trypsin. These studies illustrate how a variety of electron microscopic techniques may be utilized alone or in combination to reveal hitherto undescribed fine structure of viral particles.

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