title: Chlorella virus PBCV-1 encodes a functional homospermidine synthase.
abstract: Sequence analysis of the 330-kb genome of chlorella virus Paramecium bursaria chlorella virus 1 (PBCV-1) revealed an open reading frame, A237R, that encodes a protein with 34% amino acid identity to homospermidine synthase from Rhodopseudomonas viridis. Expression of the a237r gene product in Escherichia coli established that the recombinant enzyme catalyzes the NAD(+)-dependent formation of homospermidine from two molecules of putrescine. The a237r gene is expressed late in PBCV-1 infection. Both uninfected and PBCV-1-infected chlorella, as well as PBCV-1 virions, contain homospermidine, along with the more common polyamines putrescine, spermidine, and cadaverine. The total number of polyamine molecules per virion ( approximately 539) is too small to significantly neutralize the virus double-stranded DNA (>660,000 nucleotides). Consequently, the biological significance of the homospermidine synthase gene is unknown. However, the gene is widespread among the chlorella viruses. To our knowledge, this is the first report of a virus encoding an enzyme involved in polyamine biosynthesis.
authors.affiliation: Institut fur Pharmazeutische Biologie, Technische Universitaet Braunschweig, Mendelssohnstrasse 1, Braunschweig, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Kaiser
authors.forename: M
authors.initials: M
authors.lastname: Vollmert
authors.forename: D
authors.initials: D
authors.lastname: Tholl
authors.forename: M V
authors.initials: MV
authors.lastname: Graves
authors.forename: J R
authors.initials: JR
authors.lastname: Gurnon
authors.forename: W
authors.initials: W
authors.lastname: Xing
authors.forename: A D
authors.initials: AD
authors.lastname: Lisec
authors.forename: K W
authors.initials: KW
authors.lastname: Nickerson
authors.forename: J L
authors.initials: JL
authors.lastname: Van Etten
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D002708:Chlorella / Q000821:virology*; D004247:DNA / Q000032:analysis; D004279:DNA, Viral / Q000032:analysis / Q000235:genetics; D005814:Genes, Viral; D008969:Molecular Sequence Data; D009955:Ornithine Decarboxylase / Q000378:metabolism; D017862:Phycodnaviridae / Q000201:enzymology* / Q000235:genetics*; D010935:Plant Diseases / Q000821:virology*; D011073:Polyamines / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013095:Spermidine / Q000096:biosynthesis; D014771:Virion
chemical_list: D004279:DNA, Viral; D011073:Polyamines; D011994:Recombinant Proteins; D004247:DNA; D019883:Alkyl and Aryl Transferases; C028376:homospermidine synthetase; D009955:Ornithine Decarboxylase; D013095:Spermidine