Translation initiation factor 4E (eIF4E) binds to the m7GTP cap structure of eukaryotic mRNAs and influences the overall rates of translation. The eIF4E protein is subject to regulation at a number of levels that allow it to modulate translation of maternal mRNAs in early embryos before the onset of zygotic transcription. In zebrafish eIF4E (zeIF4E) mRNA levels are elevated in specific tissues and at specific times during embryogenesis. We have characterized the organization of the zeIF4E gene to facilitate elucidation of the molecular mechanisms that influence its expression. The zeIF4E gene spans about 14 kb and like its human counterpart is comprised of seven exons. Alternative splicing between the first and second exon generates two mRNA splice-forms called SF1 and SF2. Nuclease-S1-protection and primer-extension reveal two zeIF4E transcriptional start-sites. Transcripts initiating from the distal start-site during oogenesis are exclusively SF1, while initiation from the proximal start-site generates both splice-forms. Although translation in vitro of SF1 mRNA gives rise to a protein consistent in mass with affinity-purified zeIF4E, SF2 mRNA does not. Instead, SF2 mRNA inhibits in vitro protein synthesis in a concentration-dependent manner, suggesting it functions as a translational attenuator. Thus, specific transcriptional activation from the distal start-site may provide a unique mechanism for transcriptional regulation of the levels, as well as the function of zeIF4E mRNAs.
|Number of pages
|Published - 2000
Bibliographical noteFunding Information:
Acknowledgements We are grateful to Tad Sonstegard, Karl Clark, and Tyson Sharp for useful comments. Thanks to Mark O. Dahl-quist for expert technical help. S.C.F. was supported by Minnesota Sea Grant USDOC/NA 46RG0101–02. This work was supported by NIH grant RO1-RR06625 to P.B.H. and MCB-9808401 to R.J.
Copyright 2017 Elsevier B.V., All rights reserved.
- Nuclease S1 protection
- Translational initiation