recognized as an important biological phenomenon 
and evolutionary tool for RNA viruses. During the 
past year the laboratory developed an RNA recombi- 
nation system in which recombination occurs be- 
tween viral genomic RNA and a transfected RNA 
fragment. This system not only provides insight into 
the mechanism of RNA recombination but may also 
prove to be a new genetic engineering tool for RNA 
viruses. 
Dr. Lai and his colleagues are also interested in 
the neuropathogenesis of MHV, which is a model 
system for neurotropic viral infection. They exam- 
ined the question of virus receptor and virus entry 
mechanisms in the central nervous system of mice 
and noted that MHV utilizes two different carcino- 
embryonic antigens (CEAs) as alternative receptors 
in liver or brain — the first virus to be shown to uti- 
lize two different receptors in different tissues. A 
resistant mouse strain was discovered that has a 
functional viral receptor but is resistant to viral in- 
fection. Furthermore, they found several cell lines 
that have functional viral receptors but are selec- 
tively resistant to certain MHV strains. Thus they 
have identified the requirement of a second cellular 
factor for virus entry into cells. This factor may in- 
teract with the viral receptor and control the target 
cell specificity of the virus. The nature of this sec- 
ond factor is being studied in Dr. Lai's laboratory. 
(This part of the work is supported by a research 
grant from the National Institutes of Health.) 
Dr. Lai is also Professor of Microbiology and 
Neurology at the University of Southern Califor- 
nia School of Medicine, Los Angeles. 
Books and Chapters of Books 
Lai, M.M.C., and Stohlman, S.A. 1992. Molecular 
basis of neuropathogenicity of mouse hepatitis 
virus. In Molecular Neurovirology: Pathogenesis 
of Viral CNS Lnfections (Roos, R.P., Ed.). To- 
towa, NJ: Humana, pp 319-348. 
Articles 
Banner, L.R., and Lai, M.M.C. 1991. Random na- 
ture of coronavirus RNA recombination in the ab- 
sence of selection pressure. Virology 185:441- 
445. 
La Monica, N., Yokomori, K., and Lai, M.M.C. 
1992. Coronavirus mRNA synthesis: identifica- 
tion of novel transcription initiation signals 
which are differentially regulated by different 
leader sequences. Virology 188:402-407. 
Lai, M.M.C. 1992. Genetic recombination in RNA 
viruses. Curr Top Microbiol Lmmunol 176:21- 
32. 
Lai, M.M.C. 1992. RNA recombination in animal 
and plant viruses. Microbiol Rev 56:61-79- 
Lai, M.M.C, Lee, C.-M., Bih, F.-Y., and Govindara- 
jan , S . 1991. The molecular basis of heterogeneity 
of hepatitis delta virus, f Hepatol 13:5121-5124. 
Lee, C.-M., Bih, F.-Y., Chao, Y.-C, Govindarajan, S., 
and Lai, M.M.C. 1992. Evolution of hepatitis 
delta virus RNA during chronic infection. Virol- 
ogy 188:265-273. 
Wang, F.-I., Fleming, J.O., and Lai, M.M.C. 1992. 
Sequence analysis of the spike protein gene of mu- 
rine coronavirus variants: study of genetic sites 
affecting neuropathogenicity. Virology 186: 
742-749. 
Wu, H.-N., Wang, Y.-J., Hung, C.-F., Lee, H.-J., and 
Lai, M.M.C. 1992. Sequence and structure of the 
catalytic RNA of hepatitis delta virus genomic 
RNA. /Mo/ Biol 223:233-245. 
Xia, Y.-P., Yeh, C.-T., Ou, J.-H., and Lai, M.M.C. 
1992. Characterization of nuclear targeting signal 
of hepatitis delta antigen: nuclear transport as a 
protein complex. / Virol 66:914-921. 
Yokomori, K., Baker, S.C., Stohlman, S.A., and Lai, 
M.M.C. 1992. Hemagglutinin-esterase-specific 
monoclonal antibodies alter the neuropathogeni- 
city of mouse hepatitis virus. / Virol 66:2865- 
2974. 
Yokomori, K., Banner, L.R., and Lai, M.M.C. 
1992. Coronavirus mRNA transcription: UV light 
transcriptional mapping studies suggest an early 
requirement for a genomic-length template. / 
Virol 66:4671-4678. 
Yokomori, K., and Lai, M.M.C. 1991 ■ Mouse hepa- 
titis virus S RNA sequence reveals that nonstruc- 
tural proteins ns4 and ns5a are not essential for 
murine coronavirus replication. / Virol 65: 
5605-5608. 
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