ST-2, a telomere and subtelomere duplex and G-strand binding protein activity in Trypanosoma brucei.
From Trypanosoma brucei, we identified ST-2, a protein complex that interacts with telomeric DNA and exhibits novel features. It binds specifically to the double-stranded telomere repeats (TTAGGG) and more tightly to the subtelomere 29-base pair elements that separate the telomere repeats from their proximal telomere-associated sequences. Interestingly, ST-2 showed still greater affinity for the G-rich strand of the telomere present either as an overhang or in a single-stranded form, but it exhibited the highest affinity for the G-rich strand of the subtelomere repeats. The binding characteristics of ST-2 are complementary to those of ST-1, a 39-kDa polypeptide we previously identified in T. brucei (Eid, J., and Sollner-Webb, B. (1995) Mol. Cell. Biol. 15, 389-397) that binds preferentially to the C-rich strands of the subtelomere and telomere repeats. UV cross-linking revealed five polypeptides of ST-2 that bind directly to the G-rich strand of the DNA, one of which is phosphorylated. Furthermore, the presence of ST-1 is critical for ST-2 complex binding both to the G-rich strand and to the duplex DNA, evidently as part of the ST-2 complex. This indicates that when binding to the duplex subtelomere and telomere repeats, ST-2 may act as a protein bridge with its ST-1 subunit binding to the C-rich strand and its five other cross-linkable polypeptides binding to the G-rich strand. Such an association could serve to hold the genomic subtelomeric and telomeric sequences in a partially single-stranded configuration to facilitate the recombinational events in this region that are crucial to the parasite.
Eid
J E
JE
Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Sollner-Webb
B
B
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002846:Chromatography, Affinity; D016054:DNA, Protozoan / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000494:pharmacology; D015800:Protozoan Proteins / Q000378:metabolism*; D012091:Repetitive Sequences, Nucleic Acid; D016615:Telomere / Q000502:physiology*; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism*
D016054:DNA, Protozoan; D004268:DNA-Binding Proteins; D009838:Oligodeoxyribonucleotides; D015800:Protozoan Proteins; D019204:GTP-Binding Proteins