title: Does HIV-1 mRNA 5'-untranslated region bear an internal ribosome entry site?
abstract: Unspliced human immunodeficiency virus-1 (HIV-1) mRNA is capped and therefore can be translated via conventional scanning mechanism. In addition, its 5' untranslated region (5'UTR) is thought to function as an internal ribosome entry site (IRES) during G2/M-phase of cell cycle or when cap-dependent translation is inhibited. Recently, customary methods of internal initiation demonstrating have been challenged, and consequently existence of certain IRESs of cellular origin has been put under question. Since a precise knowledge of translation initiation mechanism used by HIV may be important for cure development, presence of the IRES in HIV-1 mRNA demands a careful reexamination using contemporary stringent criteria. The key point of our strategy is to compare translation efficiency of bicistronic mRNA bearing HIV-1 unspliced mRNA 5' UTR in the intercistronic position to that of the corresponding capped monocistronic mRNA. This approach allows determination of internal initiation contribution into the overall level of particular mRNA translation. We found that both in cell-free systems and in cultured cells monocistronic mRNA with HIV-1 unspliced mRNA 5'UTR is translated significantly better than bicistronic one. Importantly, it is also true for G2/M-phase stalled cells or for cells under conditions of inhibited cap-dependent translation. Thus, in our hands contribution of internal ribosome entry into the overall level of translation driven by HIV-1 unspliced mRNA 5'UTR is negligible, and 5'-dependent scanning is a primary mechanism of its translation initiation.
authors.affiliation: School of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow, 119234, Russia; Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia. Electronic address: alphatetia@gmail.com.
authors.forename: Victoria V
authors.initials: VV
authors.lastname: Smirnova
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia; Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 119991, Russia. Electronic address: terenin@genebee.msu.ru.
authors.forename: Ilya M
authors.initials: IM
authors.lastname: Terenin
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia. Electronic address: bioingenier@gmail.com.
authors.forename: Anastasia A
authors.initials: AA
authors.lastname: Khutornenko
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia. Electronic address: cycloheximide@yandex.ru.
authors.forename: Dmitri E
authors.initials: DE
authors.lastname: Andreev
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia; Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 119991, Russia. Electronic address: dmitriev_sergey@genebee.msu.ru.
authors.forename: Sergey E
authors.initials: SE
authors.lastname: Dmitriev
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia. Electronic address: shatsky@genebee.msu.ru.
authors.forename: Ivan N
authors.initials: IN
authors.lastname: Shatsky
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D002460:Cell Line; D015497:HIV-1 / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D000067556:Internal Ribosome Entry Sites / Q000235:genetics*; D019169:Jurkat Cells / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics
chemical_list: D020121:5' Untranslated Regions; D000067556:Internal Ribosome Entry Sites; D012333:RNA, Messenger
keywords: 5’-dependent translation; Bicistronic assay; Cap-independent translation; HIV-1; IRES; RNA-transfection