Joel G. Belasco
Professor, Skirball Institute of Biomolecular Medicine, Structural Biology; Department of Microbiology. Coord Structural Biology Program
Ph.D., 1980 Harvard University
mRNA degradation, RNA pyrophosphohydrolase, ribonuclease, translation, miRNA
Skirball Institute of Biomolecular Medicine
540 First Avenue 3rd floor, Lab 2-3
New York, N.Y. 10016
Office Tel: (212) 263-5409
Lab Tel: (212) 263-5404
Fax: (212) 263-8951
Tel: (212) 263-6282
Post-transcriptional gene regulation
Post-transcriptional processes play a crucial role in controlling gene expression in all organisms. The research in the Belasco laboratory is aimed at elucidating the molecular mechanisms by which such control is imposed. We are particularly interested in understanding how gene expression is regulated by mRNA degradation. The goal of these investigations is to identify and characterize the proteins, RNA elements, and molecular mechanisms that govern this key regulatory process in bacterial and mammalian cells.
In bacteria, the lifetimes of mRNAs can differ by more than an order of magnitude, with profound consequences for gene expression. For many years it had been assumed that bacterial mRNA degradation begins with endonucleolytic cleavage at internal sites. However, our recent findings have challenged that view by showing that mRNA decay can instead be triggered by a prior non-nucleolytic event that marks transcripts for rapid turnover: the rate-determining conversion of the 5' terminus from a triphosphate to a monophosphate. In Escherichia coli, this modification creates better substrates for the endonuclease RNase E, whose cleavage activity is greatly enhanced when the RNA 5' end is monophosphorylated, whereas in Bacillus subtilis it triggers 5'-exonucleolytic degradation by RNase J. In both species, we have identified the pyrophosphate-removing hydrolase (RppH) responsible for that 5'-terminal event, the first such bacterial enzyme ever characterized. The inability of this RNA pyrophosphohydrolase to modify 5' ends that are structurally sequestered by a stem-loop helps to explain the stabilizing influence of 5'-terminal base pairing on mRNA lifetimes in vivo.
We are also investigating mRNA degradation in human cells, with an emphasis on mRNA destabilization by microRNAs and cytoplasmic endonucleases. In animal cells, microRNAs act by annealing to mRNAs to which they are partially complementary. Our studies in human cells have demonstrated that microRNAs inhibit gene expression not only by repressing translation but also by directing rapid poly(A) tail removal, thereby hastening mRNA degradation. We have further shown that CCR4-NOT is the deadenylase whose action is stimulated by the multiprotein complex (RISC) that accompanies microRNAs to their mRNA targets. In view of growing evidence that endonucleases also play a key role in mRNA degradation in human cells, we have recently begun a comprehensive examination of human mRNAs and their decay intermediates. The goal of these collaborative experiments, based on high-throughput RNA sequencing, is to identify and characterize the many human transcripts whose degradation is governed by specific cellular endonucleases.
- An RNA pyrophosphohydrolase triggers 5’-exonucleolytic degradation of mRNA in Bacillus subtilis. Richards J, Liu Q, Pellegrini O, Celesnik H, Yao S, Bechhofer DH, Condon C, Belasco JG. Mol. Cell 43: 940-949 (2011)PMID: 21925382
- All things must pass: contrasts and commonalities in eukaryotic and bacterial mRNA decay. Belasco JG. Nat. Rev. Mol. Cell Biol. 11: 467-478 (2010) PMID: 20520623
- The bacterial enzyme RppH triggers messenger RNA degradation by 5’ pyrophosphate removal. Deana A, Celesnik H, Belasco JG. Nature 451: 355-358 (2008) PMID: 18202662
- Initiation of RNA decay in Escherichia coli by 5’ pyrophosphate removal. Celesnik H, Deana A, Belasco JG. Mol. Cell 27: 79-90 (2007) PMID: 17612492
- MicroRNAs direct rapid deadenylation of mRNA. Wu L, Fan J, Belasco JG. Proc. Natl. Acad. Sci. USA 103: 4034-4039 (2006) PMID: 16495412