Evaluation of translation initiation features of satellite tobacco necrosis virus RNA

Satellite tobacco necrosis virus RNA (STNV RNA) is an unusual mRNA that is efficiently translated in the absence of a 5$\sp\prime$-terminal cap structure and initiator AUG codon. The translational properties, in wheat germ in vitro translation system, of transcript STNV RNAs (tSTNV RNAs), with modifications to the initiator AUG codon and the 5$\sp\prime$-terminal sequences normally involved in a stem and loop structure, demonstrate that substituting CCC for the normal initiator AUG codon and eliminating the first twelve nucleotides of STNV RNA reduce the translational efficiency of the transcripts and alter the site of translation initiation. The translation of these same modified tSTNV RNAs is not dependent on the presence of a 5$\sp\prime$-terminal cap structure demonstrating that some of the features of STNV RNA that govern efficient translation and the ability to support initiation of translation in the absence of an initiator AUG codon are separate from features of STNV RNA that govern cap-independence. Translational properties of heterologous transcript mRNAs with the STNV RNA 5$\sp\prime$-untranslated leader substituted for their normal 5$\sp\prime$-untranslated leader demonstrate that the 5$\sp\prime$-untranslated leader of STNV RNA from position 13 to 30 does not confer cap-independence on heterologous transcript mRNAs but does enhance the translational efficiency of some heterologous transcript mRNAs. An 18S ribosomal RNA complementary region in the 5$\sp\prime$-untranslated leader of STNV RNA may be involved in an 18S rRNA/STNV RNA hybridization mechanism of translation initiation. Translational studies of $\beta$-glucuronidase transcripts with their 5$\sp\prime$-untranslated leaders replaced with the 5$\sp\prime$-untranslated leader of STNV RNA, modified to eliminate possible hybridization with 18S rRNA, demonstrate that the 18S rRNA complementary site in the 5$\sp\prime$-untranslated leader of STNV RNA is important for efficient translation of these transcripts and support the proposal that an 18S rRNA/mRNA hybridization mechanism is involved in initiation of translation of STNV RNA. All of the results presented in this thesis indicate that there are features of eucaryotic mRNAs, other than the initiator AUG codon and its flanking context, that determine the translational properties of eucaryotic mRNAs.U of I OnlyETDs are only available to UIUC Users without author permissio