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Journal of Virology, July 1999, p. 5722-5730, Vol. 73, No. 7
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

A Complex Translational Program Generates Multiple Novel Proteins from the Latently Expressed Kaposin (K12) Locus of Kaposi's Sarcoma-Associated Herpesvirus

Robert Sadler,1,2 Lijun Wu,3 Bagher Forghani,3 Rolf Renne,1,2 Weidong Zhong,1,2 Brian Herndier,4 and Don Ganem1,2,5,*

Howard Hughes Medical Institute1 and Departments of Microbiology,2 Medicine,5 and Pathology,4 University of California, San Francisco, California 94143, and Viral and Rickettsial Disease Laboratory, Division of Communicable Disease Control, California State Department of Health Services, Berkeley, California 947043

Received 16 February 1999/Accepted 15 April 1999

The most abundantly expressed latent transcripts encoded by the Kaposi's sarcoma (KS)-associated herpesvirus derive from the genomic region surrounding open reading frame (ORF) K12 (kaposin A). Here we show that these transcripts, initially described as limited to ORF K12 itself, more frequently encompass upstream sequences spanning two sets of 23-nucleotide GC-rich direct repeats (DRs) (DR1 and DR2). Although the DRs lack AUG codons and were previously presumed to be noncoding, a monoclonal antibody raised to infected cells detected multiple polypeptides encoded by this region. These proteins are expressed during latency and upon induction of lytic viral replication in both primary effusion lymphoma (PEL) cell lines and KS tumors. Biochemical and genetic analyses reveal that these proteins are derived from variant translational initiation at CUG codons. The predominant translation product in the PEL cell line BCBL-1 derives from the 5'-most CUG codon in the transcript, resulting in a protein (termed kaposin B) which is encoded largely by the repeats themselves and which does not include K12 sequences. Other non-AUG codons in alternate reading frames are also used at lower efficiency, including one that initiates translation of a DR-K12 fusion protein (kaposin C) that is predicted to sort to a different subcellular locale than kaposin B. Thus, the products of the K12 region, which is the most abundantly transcribed region in latency, are surprisingly complex and may encompass multiple biological functions.

* Corresponding author. Mailing address: Howard Hughes Medical Institute and Departments of Microbiology and Medicine, University of California, San Francisco, CA 94143. Phone: (415) 476-2826. Fax: (415) 476-8201. E-mail: ganem{at}socrates.ucsf.edu.

Journal of Virology, July 1999, p. 5722-5730, Vol. 73, No. 7
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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