Professor Emeritus of Biological Chemistry
Johns Hopkins University School of Medicine
JHU School of Medicine
725 N. Wolfe St. 402 Biophysics
Eukaryotic nuclear events: 1- massive sequence changes by RNA editing, and 2- a novel localization process for critical DNA sequences
Although over 10,000 papers use transient transfection, no one had looked where this DNA goes; its investigation has led to the discovery of an unprecedented sequence-specific DNA localization process that evidently also function on the cell's chromosomal DNA. It turns out that transiently transfected mammalian cells take up thousands of plasmid molecules, and they can self-associate and localize to particular subnuclear sites, in a promoter-specific manner. Plasmids bearing RNA pol I transcriptional control elements (rRNA gene promoters, enhancers, or terminators) target to sites within nucleoli, juxtaposed to the cell's rRNA genes; plasmids bearing pol III promoters target to novel peri-nucleolar sites where the cell's 5S RNA genes turn out to reside; and plasmids bearing pol II promoters go to nucleoplasmic foci, preferentially juxtaposed to chromosomal copies of those promoters. This localization does not require transcription, and can be reproduced in microinjected cells and in vitro using isolated nucleoli. This system provide a manipulatable method to study nuclear DNA localization, a topic that is receiving a much deal of attention in the recent literature (from 4C-based studies that reveal preferential locations of chromosomal genes but are not well-suited to investigating the underlying mechanism). Study of this promoter-specific localization promises to help explain how the eukaryotic cell organizes its chromosomal DNA.
In parallel, we have been studying RNA editing in trypanosomes, a fascinating form of RNA maturation in which U residues are specifically inserted into and deleted from primary transcripts, often in massive amounts, to generate mature mRNAs. We have purified a simple protein complex that actively catalyzes both U-insertional and U-deletional editing cycles, cloned their encoding genes, and optimized editing to increase U-deletion by 100 fold and U-insertion several fold. Toward elucidating the mechanism of this processing, we are biochemically analyzing the editing complex and genetically investigating (using classical knock-outs and RNAi) the genes encoding its components. Interestingly, the U-deletion and U-insertion use completely different catalytic components located in a common complex.
Law JA, O'Hearn S, Sollner-Webb B.
(2007) In Trypanosoma brucei RNA editing, TbMP18 (band VII) is critical for editosome integrity and for both insertional and deletional cleavages. Mol Cell Biol.27: 777-87.PubMed Reference
Zhelonkina AG, O'Hearn SF, Law JA, Cruz-Reyes J, Huang CE, Alatortsev VS, Sollner-Webb B.
(2006) T. brucei RNA editing: action of the U-insertional TUTase within a U-deletion cycle. RNA. 12: 476-87.PubMed Reference
Law, J., Huang, C., O'Hearn, S., and Sollner-Webb, B.
(2005) In Trypanosoma brucei RNA editing, band II enables recognition specifically at each step of the U insertion cycle. Mol Cell Biol. 2005 Apr;25(7):2785-94.PubMed Reference
O'Hearn, S., Huang, C., Hemann, M., Zhelonkina, A., and Sollner-Webb, B.
(2003) Trypanosoma brucei RNA editing complex: band II is structurally critical and maintains band V ligase, which is nonessential.Mol Cell Biol. 2003 Nov;23(21):7909-19.PubMed Reference
Huang, C., O'Hearn, S. and Barbara Sollner-Webb.
(2002) Assembly and function of the RNA editing complex in Trypanosoma brucei requires band III protein. Mol. Cell. Biol. 22, 3194-3203.PubMed Reference
Cruz-Reyes, J., Zhelonkina, A., Huang, C. and Sollner-Webb, B.
(2002) Distinct functions of two RNA ligases in active T. brucei RNA editing complexes. Mol. Cell. Biol. 22: 4652-4660.PubMed Reference
Cruz-Reyes, J., Zhelonkina, A., Rusche, L. and Sollner-Webb, B.
(2001) Trypanosome RNA editing: Simple guide RNA features enhance U deletion 100 fold. Mol. Cell. Biol. 21, 884-892.PubMed Reference
Huang, C., Cruz-Reyes, J., Zhelonkina, A,. O'Hearn, S., Wirtz, E., and Sollner-Webb, B.
(2001) The two RNA ligases of the T. brucei. Roles for ligases in the RNA editing complex of Trypanosoma brucei: band IV is needed for U-deletion and RNA repair. EMBO J. 20, 4694-4704.PubMed Reference
Cruz-Reyes, J., Rusche, L., Piller, K., and Sollner-Webb, B.
(1998) Trypanosoma brucei RNA editing: adenosine nucleotides inversely affect U-deletion and U-insertion reactions at mRNA cleavage. Mol. Cell 1, 401-409.PubMed Reference
Lazdins, I., Delannoy, M., and Sollner-Webb, B.
(1997) Analysis of nucleolar transcription and processing domains and pre-rRNA movements by in situ hybridization. Chromosoma. 105, 481-495.PubMed Reference
Rusche, L., Cruz-Reyes, J., Piller, K., and Sollner-Webb, B.
(1997) Purification of a functional enzymatic editing complex from Trypanosoma brucei mitochondria. EMBO J. 16, 4069-4081.PubMed Reference