title: A La autoantigen homologue is required for the internal ribosome entry site mediated translation of giardiavirus.
abstract: Translation of Giardiavirus (GLV) mRNA is initiated at an internal ribosome entry site (IRES) in the viral transcript. The IRES localizes to a downstream portion of 5' untranslated region (UTR) and a part of the early downstream coding region of the transcript. Recent studies indicated that the IRES does not require a pre-initiation complex to initiate translation but may directly recruit the small ribosome subunit with the help of a number of trans-activating protein factors. A La autoantigen homologue in the viral host Giardia lamblia, GlLa, was proposed as one of the potential trans-activating factors based on its specific binding to GLV-IRES in vitro. In this study, we further elucidated the functional role of GlLa in GLV-IRES mediated translation in Giardia by knocking down GlLa with antisense morpholino oligo, which resulted in a reduction of GLV-IRES activity by 40%. An over-expression of GlLa in Giardia moderately stimulated GLV-IRES activity by 20%. A yeast inhibitory RNA (IRNA), known to bind mammalian and yeast La autoantigen and inhibit Poliovirus and Hepatitis C virus IRES activities in vitro and in vivo, was also found to bind to GlLa protein in vitro and inhibited GLV-IRES function in vivo. The C-terminal domain of La autoantigen interferes with the dimerization of La and inhibits its function. An over-expression of the C-terminal domain (200-348aa) of GlLa in Giardia showed a dominant-negative effect on GLV-IRES activity, suggesting a potential inhibition of GlLa dimerization. HA tagged GlLa protein was detected mainly in the cytoplasm of Giardia, thus supporting a primary role of GlLa in translation initiation in Giardiavirus.
authors.affiliation: Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, United States of America.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Garlapati
authors.forename: Ashesh A
authors.initials: AA
authors.lastname: Saraiya
authors.forename: Ching C
authors.initials: CC
authors.lastname: Wang
mesh_terms: D000953:Antigens, Protozoan / Q000737:chemistry / Q000378:metabolism*; D001324:Autoantigens / Q000737:chemistry*; D001483:Base Sequence; D003593:Cytoplasm / Q000378:metabolism; D055785:Gene Knockdown Techniques; D016829:Giardia lamblia / Q000166:cytology / Q000276:immunology / Q000821:virology; D019198:Giardiavirus / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012331:RNA, Fungal / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D000953:Antigens, Protozoan; D001324:Autoantigens; D012331:RNA, Fungal