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Two mouse lines transgenic with the human poliovirus receptor gene (PVR), TGM-PRG-1 and TGM-PRG-3, were characterized to determine whether transgene copy number and PVR expression levels influence susceptibility to poliovirus. The mouse lines have been bred for more than 10 generations and the transgene was stably transmitted to progeny as determined by Southern blot hybridization and restriction fragment length polymorphism. The transgene copy number is 10 in the TGM-PRG-3 mouse line and one in the TGM-PRG-1 mouse line. Abundance of PVR RNA is on average three-fold higher in TGM-PRG-3 relative to TGM-PRG-1 tissues, and the abundance of the receptor molecule is three-fold higher in TGM-PRG-3 central nervous system tissues compared to TGM-PRG-1 tissues as determined by Western blot analysis. When TGM-PRG-1 and TGM-PRG-3 mice were inoculated intracranially with a neurovirulent type III poliovirus strain, they developed clinical symptoms and CNS lesions characteristic of human poliomyelitis. These results indicate that the PVR gene is expressed as a functional receptor in the CNS of both mouse lines rendering the mice susceptible to poliovirus infection. Even though the two mouse lines have different copy numbers of the transgene and different levels of PVR RNA and protein, they are similar in their susceptibility to poliovirus.

A complete, cloned complementary DNA copy of the RNA genome of poliovirus was constructed in the Pst I site of the bacterial plasmid pBR322. Cultured mammalian cells transfected with this hybrid plasmid produced infectious poliovirus. Cells transfected with a plasmid which lacked the first 115 bases of the poliovirus genome did not produce virus.

Poliovirus mRNA contains a long 5' noncoding region of about 750 nucleotides (the exact number varies among the three virus serotypes), which contains several AUG codons upstream of the major initiator AUG. Unlike most eucaryotic mRNAs, poliovirus does not contain a m7GpppX (where X is any nucleotide) cap structure at its 5' end and is translated by a cap-independent mechanism. To study the manner by which poliovirus mRNA is expressed, we examined the translational efficiencies of a series of deletion mutants within the 5' noncoding region of the mRNA. In this paper we report striking translation system-specific differences in the ability of the altered mRNAs to be translated. The results suggest the existence of an inhibitory cis-acting element(s) within the 5' noncoding region of poliovirus (between nucleotides 70 and 381) which restricts mRNA translation in reticulocyte lysate, wheat germ extract, and Xenopus oocytes, but not in HeLa cell extracts. In addition, we show that HeLa cell extracts contain a trans-acting factor(s) that overcomes this restriction.

Recombinants between two different influenza C viruses were isolated. In MDCK (canine kidney) cells, one strain, C/JJ/50, caused lytic plaques, whereas C/JHG/66 virus did not produce clear plaques. From a mixed infection of MDCK cells with C/JHG/66 virus and UV-inactivated C/JJ/50 virus, clones were isolated which possessed the clear-plaque phenotype. Fingerprint analyses indicated that the RNAs of parent viruses had different oligonucleotide patterns and that one of the clones derived from the mixed infection was formed by reassortment of parental genes. This recombinant clone most likely inherited RNAs 1, 2, 3, 6, and 7 from C/JGH/66 virus and RNAs 4 and 5 from C/JJ/50 virus.

It was shown that all eight RNA segments of influenza B viruses are most likely monocistronic and code for eight virus-specific polypeptides. A genetic map of the influenza B virus genome was established, and six polypeptides (P1 protein, nucleoprotein, hemagglutinin, neuraminidase, M protein, and nonstructural protein) were unambiguously assigned to specific RNA segments. Molecular weight estimates of the eight individual genes are obtained by using the glyoxal method. These results suggest that each influenza B virus RNA segment has a greater molecular weight than the influenza A virus RNA segment which codes for the analogous gene product.