title: A sequence-dependent exonuclease activity from Tetrahymena thermophila.
abstract: BACKGROUND
  Telomere function requires a highly conserved G rich 3'- overhang. This structure is formed by 5'-resection of the C-rich telomere strand. However, while many nucleases have been suggested to play a role in processing, it is not yet clear which nucleases carry out this 5'-resection.
  
  
  RESULTS
  We used biochemical purification to identify a sequence-dependent exonuclease activity in Tetrahymena thermophila cell extracts. The nuclease activity showed specificity for 5'-ends containing AA or AC sequences, unlike Exo1, which showed sequence-independent cleavage. The Tetrahymena nuclease was active on both phosphorylated and unphosphorylated substrates whereas Exo1 requires a 5'-phosphate for cleavage.
  
  
  CONCLUSIONS
  The specificities of the enzyme indicate that this novel Tetrahymena exonuclease is distinct from Exo1 and has properties required for 3'-overhang formations at telomeres.
authors.affiliation: Department of Molecular Biology and Genetics, The Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Hui-I Kao
authors.initials: HI
authors.lastname: Tom
authors.forename: Carol W
authors.initials: CW
authors.lastname: Greider
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000235:genetics / Q000378:metabolism; D005090:Exodeoxyribonucleases / Q000378:metabolism; D005092:Exonucleases / Q000378:metabolism*; D020862:GC Rich Sequence / Q000235:genetics; D009711:Nucleotides / Q000378:metabolism; D013379:Substrate Specificity; D016615:Telomere / Q000235:genetics / Q000378:metabolism; D016808:Tetrahymena thermophila / Q000166:cytology / Q000201:enzymology*
chemical_list: D009711:Nucleotides; D004247:DNA; D005090:Exodeoxyribonucleases; D005092:Exonucleases