Me. Cardenas et al., A XENOPUS EGG FACTOR WITH DNA-BINDING PROPERTIES CHARACTERISTIC OF TERMINUS-SPECIFIC TELOMERIC PROTEINS, Genes & development, 7(5), 1993, pp. 883-894
We have identified a Xenopus laevis protein factor that specifically r
ecognizes vertebrate telomeric repeats at DNA ends. This factor, calle
d Xenopus telomere end factor (XTEF), is detected predominantly in ext
racts of Xenopus eggs and ovaries, which are estimated to contain suff
icient XTEF to bind approximately 3 x 10(7) DNA ends. In contrast, XTE
F is much less abundant (approximately 90 per cell) in extracts of som
atic cell nuclei. Mobility retardation analysis of the XTEF activity i
n egg extracts indicates that this factor binds the vertebrate telomer
ic repeat sequence (TTAGGG)2 when present in a single-stranded 3' over
hang. Single-stranded 3' extensions of (TTTGGG)2, (AAAGGG)2, (TTACCC)2
, or a nonrepetitive sequence fail to bind XTEF efficiently, whereas c
hanges in the double-stranded sequence 5' to the TTAGGG repeat tail ar
e tolerated. TTAGGG repeats are not recognized at internal positions,
at a 5' protruding end, or in double-stranded DNA. In addition, the fa
ctor does not bind RNA with single-stranded UUAGGG repeats at a 3' end
. XTEF-DNA complexes form and are stable in high salt. The DNA-binding
properties of XTEF resemble the characteristics of a class of terminu
s-specific telomere proteins identified previously in hypotrichous cil
iates.