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Type Species |
(L2) |
Virions are quasi-spherical, slightly pleomorphic, enveloped, and about 80 nm (range 50-125 nm) in diameter (Fig. 1). Size varies due to virion heterogeneity; at least three distinct virion forms are produced during infection. Thin sections show virions with densely stained centers, seemingly containing condensed DNA, and particles with lucent centers. The absence of a regular capsid structure suggests the Acholeplasma phage L2 (L2) virion is an asymmetric nucleoprotein condensation bounded by a lipid-protein membrane.
Physicochemical and Physical Properties
Virions are extremely heat sensitive, relatively cold stable, and inactivated by nonionic detergents (Brij-58, Triton X-100, and Nonidet P-40), ether, and chloroform. Viral infectivity is resistant to DNase I and phospholipase A, but sensitive to pronase and trypsin treatment. UV-irradiated virions can be reactivated in host cells by excision and SOS DNA repair systems. Virions are relatively resistant to photodynamic inactivation.
Virions contain one molecule of infectious, circular, negative superhelical, dsDNA. The Acholeplasma phage L2 genome is 11,965 bp in size, with a G+C value of 32%. All ORFs are encoded in one strand. Several genes are translated from overlapping reading frames.
Virions contain at least four major proteins, with Mr about 64, 61, 58, and 19 103. Several minor protein bands are also observed in virion preparations. DNA sequence analysis indicates 15 ORFs (encoding proteins of Mr from 7 to 81 103).
Virions and host cell membranes have similar fatty acid compositions. Variation of host cell membrane fatty acid composition leads to virions with corresponding fatty acid composition variations. Data indicate viral membrane lipids are in a bilayer structure.
None reported.
Genome Organization and Replication
Acholeplasma phage L2 infection involves a noncytocidal productive infectious cycle followed by a lysogenic cycle in each infected cell. At least 11 overlapping mRNAs are transcribed from the DNA coding strand, from at least 8 promoters. See Fig. 2.
Noncytocidal infection involves progeny virus release by budding from the host cell membrane, with the host surviving as a lysogen. Lysogeny involves integration of the Acholeplasma phage L2 genome into a unique site in the host cell chromosome. Lysogens are resistant to superinfection by homologous virus but not by heterologous virus (apparently due to a repressor), and are inducible by UV-irradiation and mitomycin C.
Acholeplasma phage L2 infects Acholeplasma laidlawii strains: other possible plasmaviruses have been reported to infect A. modicum and A. oculi strains.
List of Species Demarcation Criteria in the Genus
Not applicable.
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, host names { }, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:
|
Acholeplasma phage L2 |
{A. laidlawii} |
[L13696] |
(L2) |
Tentative Species in the Genus
|
Acholeplasma phage v1 |
{A. laidlawii} |
(v1) |
|
Acholeplasma phage v2 |
{A. laidlawii} |
(v2) |
|
Acholeplasma phage v4 |
{A. laidlawii} |
(v4) |
|
Acholeplasma phage v5 |
{A. laidlawii} |
(v5) |
|
Acholeplasma phage v7 |
{A. laidlawii} |
(v7) |
|
Acholeplasma phage M1 |
{A. modicum} |
(M1) |
|
Acholeplasma phage O1 |
{A. oculi} |
(O1) |
List of Unassigned Viruses in the Family
None reported.
Phylogenetic Relationships within the Family
Not available.
None reported.
Plasma: from Greek plasma, “shaped product”.
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