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Journal of Virology, July 2001, p. 6016-6021, Vol. 75, No. 13
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.13.6016-6021.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Proper Processing of Avian Sarcoma/Leukosis Virus Capsid Proteins Is Required for Infectivity

Yan Xiang,^1, Rebekah Thorick,¹ Marcy L. Vana,¹ Rebecca Craven,² and Jonathan Leis^3,*

Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4935¹; Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033²; and Northwestern University School of Medicine, Chicago, Illinois 60611³

Received 27 September 2000/Accepted 9 April 2001

The formation of the mature carboxyl terminus of CA in avian sarcoma/leukemia virus is the result of a sequence of cleavage events at three PR sites that lie between CA and NC in the Gag polyprotein. The initial cleavage forms the amino terminus of the NC protein and releases an immature CA, named CA1, with a spacer peptide at its carboxyl terminus. Cleavage of either 9 or 12 amino acids from the carboxyl terminus creates two mature CA species, named CA2 and CA3, that can be detected in avian sarcoma/leukemia virus (R. B. Pepinsky, I. A. Papayannopoulos, E. P. Chow, N. K. Krishna, R. C. Craven, and V. M. Vogt, J. Virol. 69:6430-6438, 1995). To study the importance of each of the three CA proteins, we introduced amino acid substitutions into each CA cleavage junction and studied their effects on CA processing as well as virus assembly and infectivity. Preventing cleavage at any of the three sites produced noninfectious virus. In contrast, a mutant in which cleavage at site 1 was enhanced so that particles contained CA2 and CA3 but little detectable CA1 was infectious. These results support the idea that infectivity of the virus is closely linked to proper processing of the carboxyl terminus to form two mature CA proteins.

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^* Corresponding author. Mailing address: Department of Microbiology and Immunology, Northwestern University School of Medicine, 303 E. Chicago Ave., Chicago, IL 60611. Phone: (312) 503-0338. Fax: (312) 503-7654. E-mail: j-leis{at}northwestern.edu.

Present address: NIH/NIAID/LVD, Bethesda, MD 20892-0445.

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Journal of Virology, July 2001, p. 6016-6021, Vol. 75, No. 13
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.13.6016-6021.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

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