L. Singh et al., SEX-SPECIFIC AND TISSUE-SPECIFIC BKM(GATA)-BINDING PROTEIN IN THE GERM-CELLS OF HETEROGAMETIC SEX, The Journal of biological chemistry, 269(41), 1994, pp. 25321-25327
The ZZ male/ZW female system of sex determination (female heterogamety
) is found in snakes and birds whereas XY male/XX female system of sex
determination (male heterogamety) operates in mammals including human
s. The W and Y chromosomes are largely heterochromatic and undergo cyc
les of condensation and decondensation in the germ cells of ovary and
testis, respectively, whereas they remain highly condensed and transcr
iptionally inactive in all somatic cells. Both chromosomes have enrich
ed stretches of GATA repeats along their entire length (which is ident
ified as banded krait minor satellite DNA and called Bkm) that are hig
hly conserved through widely separated orders of eukaryotes. Here we r
eport the existence of a factor, which specifically binds to Bkm, in t
he germ cells of the heterogametic sex (ovary in female heterogamety a
nd testis in male heterogamety) where decondensation (activation) of t
he W and Y chromosomes, respectively, occurs; it has been purified as
a polypeptide of 57.5 kDa from the rat snake ovary and designated as B
km-binding protein (BBP) by virtue of its binding to GATA repeats of B
km. Such a sex- and tissue specific BBP is also present in the ovary o
f other species of snakes and in the testis of mouse and human where t
he Y chromosome is highly decondensed. We suggest that GATA repeats of
Bkm brings about a coordinated decondensation of the W and Y sex chro
mosomes in the germ cells of the heterogametic sex in response to BBP
which may serve as a ''switch'' for the activation of the genes presen
t on the W and Y chromosomes.