Translation of the human LINE-1 element, L1Hs.
Full-length RNA transcribed from the human LINE-1 (L1) element L1 Homo sapiens (L1Hs) has a 900-nt, G+C-rich, 5'-untranslated region (UTR). The 5' UTR is followed by two long open reading frames, ORF1 and ORF2, which are separated from each other by an inter-ORF region of 33 nt that includes two or three in-frame stop codons. We examine here the mechanism(s) by which the translation of L1Hs ORF1 and ORF2 is initiated. A stable hairpin structure (delta G = -74.8 kcal/mol), inserted at nt 661 of the 5' UTR, caused a 3- to 8-fold decrease in the in vitro and in vivo translation of either a lacZ reporter gene for ORF1 or the ORF1 polypeptide product, p40, but translation of a lacZ reporter gene in ORF2 was increased. The results are compatible with a model for ORF1 translation initiation in which the majority of ribosomes scan from a point 5' of nt 661 but suggest that ORF2 is not translated by attached ribosomes that reinitiate after the termination of ORF1 translation. Our data are compatible with a model whereby the translation of L1Hs ORF2 is initiated internally.
McMillan
J P
JP
Laboratory of Biochemistry, National Cancer Institute, Bethesda, MD 20892.
Singer
M F
MF
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002151:Calorimetry; D002460:Cell Line; D003062:Codon / Q000235:genetics; D005796:Genes; D015186:Hominidae / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides; D016366:Open Reading Frames; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D015183:Restriction Mapping; D014158:Transcription, Genetic; D014162:Transfection; D001616:beta-Galactosidase / Q000096:biosynthesis
D003062:Codon; D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger; D001616:beta-Galactosidase