{
   "source_x": "PMC",
   "title": "Structural Analysis of the \u22121 Ribosomal Frameshift  Elements in Giardiavirus mRNA",
   "doi": "http://dx.doi.org/10.1128/JVI.75.22.10612-10622.2001",
   "pmcid": "PMC114643",
   "abstract": "The RNA polymerase of giardiavirus (GLV) is synthesized as a fusion protein through a \u22121 ribosomal frameshift in a region where gag and pol open reading frames (ORFs) overlap. A heptamer, CCCUUUA, and a potential pseudoknot found in the overlap were predicted to be required for the frameshift. A 68-nucleotide (nt) cDNA fragment containing these elements was inserted between the GLV 5\u2032 631-nt cDNA and the out-of-frame luciferase gene that required a \u22121 frameshift within the 68-nt fragment for expression. Giardia lamblia trophozoites transfected with the transcript of this construct showed a frameshift frequency at 1.7%, coinciding with the polymerase-to-capsid protein ratio in GLV. The heptamer is required for the frameshift but can be replaced with other sequences of the same motif. Mutations placing stop codons in the 0 or \u22121 frame, located directly before or after the heptamer, implicated the latter as the site for the \u22121 frameshift. Shortening or destroying the putative stem decreased the frameshift efficiency threefold; the efficiency was fully recovered by mutations to restore the stem. Deleting 18 nt from the 3\u2032 end of the 68-nt fragment, which formed the second stem in the putative pseudoknot, had no effect on the frequency of the frameshift. Chemical probing of the RNA secondary structure in the frameshift region showed that bases resistant to chemical modification were clustered in the putative stem structures, thus confirming the presence of the postulated stem-loop, while all the bases in the loop were chemically modified, thus ruling out their capability of forming a pseudoknot. These results confirmed the conclusion based on data from the mutation study that there is but a simple stem-loop downstream from the heptamer. Together, they constitute the structural elements for a \u22121 ribosomal frameshift in the GLV transcript.",
   "authors": [
      "['Li, Lei', 'Wang, Alice L.', 'Wang, Ching C.']"
   ],
   "id": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC114643"
}