Nucleic Acids Research, Vol 27, Issue 15 3190-3196, Copyright © 1999 by Oxford University Press
RS Anderson, FJ Bollum and KL Beattie
Terminal transferase (TdT), when incubated with a purified(32)P-5"-end-
labeled oligonucleotide of defined length in the presence of Co(2+),
Mn(2+)or Mg(2+)and 2-mercaptoethanol in cacodylate or HEPES buffer, pH 7.2,
exhibits the ability to remove a 3"-nucleotide from one oligonucleotide and
add it to the 3"-end of another. When analyzed by urea-PAGE, this activity
is observed as a disproportionation of the starting oligonucleotide into a
ladder of shorter and longer oligonucleotides distributed around the
starting material. Optimal metal ion concentration is 1-2 mM. All three
metal ions support this activity with Co(2+)> Mn(2+) congruent with
Mg(2+). Oligonucleotides p(dT) and p(dA) are more efficient substrates than
p(dG) and p(dC) because the latter may form secondary structures. The
dismutase activity is significant even in the presence of dNTP
concentrations comparable to those that exist in the nucleus during the
G(1)phase of the cell cycle. Using BetaScope image analysis the rate of
pyrophosphorolytic dismutase activity was found to be only moderately
slower than the poly-merization activity. These results may help explain
the GC-richness of immunoglobulin gene segment joins (N regions) and the
loss of bases that occur during gene rearrangements in pre-B and pre-T
cells.
ARTICLES
Pyrophosphorolytic dismutation of oligodeoxy-nucleotides by terminal deoxynucleotidyltransferase
Baylor College of Medicine, Department of Biochemistry, One Baylor Plaza, Houston TX 77030, USA. randerson@masters.edu
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