title: Multiple roles for polypyrimidine tract binding (PTB) proteins in trypanosome RNA metabolism.
abstract: Trypanosomatid genomes encode for numerous proteins containing an RNA recognition motif (RRM), but the function of most of these proteins in mRNA metabolism is currently unknown. Here, we report the function of two such proteins that we have named PTB1 and PTB2, which resemble the mammalian polypyrimidine tract binding proteins (PTB). RNAi silencing of these factors indicates that both are essential for life. PTB1 and PTB2 reside mostly in the nucleus, but are found in the cytoplasm, as well. Microarray analysis performed on PTB1 and PTB2 RNAi silenced cells indicates that each of these factors differentially affects the transcriptome, thus regulating a different subset of mRNAs. PTB1 and PTB2 substrates were categorized bioinformatically, based on the presence of PTB binding sites in their 5' and 3' flanking sequences. Both proteins were shown to regulate mRNA stability. Interestingly, PTB proteins are essential for trans-splicing of genes containing C-rich polypyrimidine tracts. PTB1, but not PTB2, also affects cis-splicing. The specificity of binding of PTB1 was established in vivo and in vitro using a model substrate. This study demonstrates for the first time that trans-splicing of only certain substrates requires specific factors such as PTB proteins for their splicing. The trypanosome PTB proteins, like their mammalian homologs, represent multivalent RNA binding proteins that regulate mRNAs from their synthesis to degradation.
authors.affiliation: Bar-Ilan University, Ramat-Gan, Israel.
authors.forename: Michael Zeev
authors.initials: MZ
authors.lastname: Stern
authors.forename: Sachin Kumar
authors.initials: SK
authors.lastname: Gupta
authors.forename: Mali
authors.initials: M
authors.lastname: Salmon-Divon
authors.forename: Tomer
authors.initials: T
authors.lastname: Haham
authors.forename: Omer
authors.initials: O
authors.lastname: Barda
authors.forename: Sarit
authors.initials: S
authors.lastname: Levi
authors.forename: Chaim
authors.initials: C
authors.lastname: Wachtel
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Nilsen
authors.forename: Shulamit
authors.initials: S
authors.lastname: Michaeli
mesh_terms: D000818:Animals; D020869:Gene Expression Profiling; D049452:Green Fluorescent Proteins / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D038941:Polypyrimidine Tract-Binding Protein / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012326:RNA Splicing; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism*; D020040:Trans-Splicing; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D038941:Polypyrimidine Tract-Binding Protein; D049452:Green Fluorescent Proteins