Arch Virol (2004) 149: 975–988
Identiﬁcation of the essential and non-essential transcription
units for protein synthesis, DNA replication and infectious
virus production of Porcine circovirus type 1
A. K. Cheung
Virus and Prion Diseases of Livestock Research Unit, National Animal
Disease Center, USDA, Agricultural Research Service, Ames, Iowa, U.S.A.
Received August 4, 2003; accepted September 29, 2003
Published online December 23, 2003
Summary. A plasmid-based transfection system capable of yielding infectious
Porcine circovirus type 1 (PCV1) was established and mutational analysis was
conducted to investigate the involvement of each viral transcription unit in protein
synthesis, DNA replication and progeny virus production. During PCV1 replica-
tion in PK15 cells, twelve viral-speciﬁc RNAs are synthesized. They include
the capsid protein RNA (CR), eight Rep-associated RNAs (Rep, Rep’, Rep3a,
Rep3b, Rep3c-1, Rep3c-2, Rep3c-3 and Rep3c-4), and three NS-associated RNAs
(NS462, NS642 and NS0). A stop codon introduced at the 5
-end of CR did not
affect Rep-associated antigens or viral DNA synthesis. Altering the consensus
dinucleotide at the splice junctions of the Rep3 RNAs and NS462 or introducing
an early termination codon in Rep3c-4 and NS0 also did not have any affect on
virus replication. However, mutations in Rep and Rep’ caused greater than 99%
reduction of protein synthesis and complete shut down of viral DNA replication.
NS642 could not be assayed in this study because silent mutation at the splice
junction was not possible. However, it is probably equivalent to the non-essential
RNA (NS672) of PCV type 2. Thus, only two proteins, Rep and Rep’, are essential
for PCV1 protein, DNA and infectious virus biosynthesis.
Porcine circovirus (PCV) is a members of the Circovirus genus [16, 23],
which also includes Beak-and-feather disease virus, Goose circovirus, Canary
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