Requirements for the translational repression of ferritin transcripts in wheat germ extracts by a 90-kDa protein from rabbit liver.
A specific repressor of ferritin mRNA translation originally detected in rabbit reticulocyte lysates has now been purified to homogeneity from rabbit liver, as described in a companion paper (Walden, W. E., Patino, M. M., and Gaffield, L. (1989) J. Biol. Chem. 264, 13765-13769). This repressor is a 90-kDa protein that binds to a sequence in the 5'-untranslated region of ferritin mRNA. In this communication we describe the molecular features of a ferritin light chain transcript that are required for the repression of its translation by this protein. Addition of small amounts of the 90-kDa ferritin repressor protein (FRP) completely inhibited translation of ferritin transcripts in a wheat germ system. This repression did not require mRNA sequences contained in the 3'-untranslated region or in the majority of the ferritin coding region. In contrast, the first 130 nucleotides of the 5'-untranslated region, which contains the 28-nucleotide "iron responsive element" (IRE), was required for the repressive effect. Moreover, repression of full length transcripts was relieved by addition of a molar excess of a 92-nucleotide transcript of the 5'-untranslated region which also contained the IRE. These results suggest that no sequence information other than a portion of the 5'-untranslated region containing the IRE sequence is required for action of the 90-kDa FRP. In addition, a quantitative comparison of the repression of transcript with that of poly(A+) RNAs indicates that no post-transcriptional modifications of the latter (other than cap addition) are involved in the action of the 90-kDa FRP.
Department of Biology, Washington University, St. Louis, Missouri 63130.
P H
PH
Brown
S
S
Daniels-McQueen
W E
WE
Walden
M M
MM
Patino
L
L
Gaffield
D
D
Bielser
R E
RE
Thach
D000818:Animals; D001483:Base Sequence; D005293:Ferritins / Q000235:genetics*; D008099:Liver / Q000502:physiology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010944:Plants / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000187:drug effects*; D011500:Protein Synthesis Inhibitors; D011506:Proteins / Q000302:isolation & purification* / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics; D011817:Rabbits; D014158:Transcription, Genetic; D014908:Triticum / Q000378:metabolism
D011500:Protein Synthesis Inhibitors; D011506:Proteins; D012333:RNA, Messenger; D005293:Ferritins