Sosnovtsev Stanislav V, Belliot Gaël, Chang Kyeong-Ok, Onwudiwe Oge, Green Kim Y
Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 50 South Drive MSC8007, Building 50, Room 6316, Bethesda, MD 20892-8007, USA.
J Virol. 2005 Apr;79(7):4012-24. doi: 10.1128/JVI.79.7.4012-4024.2005.
The third open reading frame (ORF3) located at the 3' end of the genomic RNA of feline calicivirus (FCV) encodes a small (12.2-kDa) minor structural protein of 106 amino acids designated VP2. Point mutations and deletions were introduced into an infectious FCV cDNA clone in order to evaluate the functional importance of ORF3 and its encoded protein, VP2. Deletion of the entire ORF3 sequence was lethal for the virus, and evidence was found for strong selective pressure to produce the VP2 protein. Extended deletions in the 5' end and small deletions in the 3' end of ORF3, as well as the introduction of stop codons into the ORF3 sequence, were tolerated by the viral replication machinery, but infectious virus could not be recovered. Infectious virus particles could be rescued from a full-length FCV cDNA clone encoding a nonfunctional VP2 when VP2 was provided in trans from a eukaryotic expression plasmid. Our data indicate that VP2, a protein apparently unique to the caliciviruses, is essential for productive replication that results in the synthesis and maturation of infectious virions and that the ORF3 nucleotide sequence itself overlaps a cis-acting RNA signal at the genomic 3' end.
位于猫杯状病毒（FCV）基因组RNA 3'端的第三个开放阅读框（ORF3）编码一种由106个氨基酸组成的小（12.2 kDa）次要结构蛋白，称为VP2。为了评估ORF3及其编码蛋白VP2的功能重要性，将点突变和缺失引入到一个感染性FCV cDNA克隆中。整个ORF3序列的缺失对病毒是致命的，并且发现了产生VP2蛋白的强烈选择压力的证据。ORF3 5'端的延伸缺失和3'端的小缺失，以及在ORF3序列中引入终止密码子，病毒复制机制都能容忍，但无法回收感染性病毒。当从真核表达质粒反式提供VP2时，可从编码无功能VP2的全长FCV cDNA克隆中拯救出感染性病毒颗粒。我们的数据表明，VP2是一种显然为杯状病毒所特有的蛋白，对于导致感染性病毒粒子合成和成熟的有效复制至关重要，并且ORF3核苷酸序列本身与基因组3'端的一个顺式作用RNA信号重叠。
