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The 11 th International Workshop on KSHV & Related Agents, Birmingham, UK
Lytic Replication Abstract 40
DOMAIN STRUCTURE AND FUNCTION OF KSHV ORF57 PROTEIN IN PROTEIN-
PROTEIN AND PROTEIN-RNA INTERACTIONS
Vladimir Majerciak and Zhi-Ming Zheng
HIV and AIDS Malignancy Branch, National Cancer Institute, National Institutes of Health,
10 Central Dr. 6N106, Bethesda, MD 20892-1868, USA
Abstract
Kaposi’s sarcoma-associated herpesvirus (KSHV) ORF57 is a multifunctional regulator in
the expression of viral lytic genes. ORF57 enhances the expression of both intronless and
intron-containing viral genes and is essential for virus replication. However, the
molecular mechanism of ORF57 action remains unclear. Our analysis of ORF57 amino
acid (aa) sequence identified two distinctive parts of ORF57 based on secondary structure
prediction: the N-terminal part has no obvious secondary structure (coil), but bears a
strong antigenic epitope; the C-terminal part consists of several alpha-helixes and betasheets,
with all weak antigenic epitopes. In vivo ORF57 was found in a multiprotein
complex enriched in RNA-binding proteins including RNA helicase A, hnRNP U, nucleolin,
and Aly/REF in association with RNA. The relaxed N-terminal region, in particular the
nuclear localization signal 2 (NLS2, aa 121-130) that overlaps the antigenic epitope, was
mapped to mediate these interactions. The interaction of ORF57 with nucleolin depends
on RNAs. In lyticaly infected B cells, KSHV ORF57 interacts with nucleolin in nucleoplasm,
but not colocalizes with nucleolin concentrated in nucleoli. The C-terminal structural
region of ORF57 contains a domain for ORF57 dimerization. The dimer formation between
mutant and wild-type ORF57 leads the mt ORF57 normally localized in the cytoplasm to
translocate in the nucleus in co-transfected cells. Data indicate that KSHV ORF57
associates with many protein partners through its different domains to diversify its
functions in regulating expression of viral intronless or intron-containing genes at
posttranscriptonal level.
Presenting author Email: majerciv@mail.nih.gov
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