Acquisition of fertilizability in Xenopus
coelomic eggs is correlated with the conversion from
coelomic to vitelline envelope during passage of the
eggs through the pars recta portion of oviduct. The
conversion includes processing of a major envelope
constituent gp43 of coelomic envelopes to gp41 of
vitelline envelopes by a trypsin-type protease, oviductin,
which is secreted from the pars recta. Our recent
sequencing analyses [Kubo et al., (1997): Dev Growth
Diff 39:405–411] strongly suggested that the Nterminal
portion of gp41 is exposed as a result of
oviductin digestion. In this study, a monoclonal antibody
specific to the predicted N-terminus of gp41 was raised
by immunizing mice with a synthetic N-terminal hexapeptide
(QLPVSP) coupled to keyhole limpet hemocyanin.
The antibody specifically reacted to gp41, but not to
gp43, indicating that Gln62 is exposed as the Nterminal
amino acid of gp41 by oviductin-mediated
cleavage of gp43 at Arg61 in GSR61. The C-terminal
sequencing of gp43 and gp41 indicated that Arg373
in GSR373 as the C-terminus of gp41 is generated by
cleavage of three amino acid (WNQ) residues from the
C-terminus of gp43. The resulting polypeptide moiety of
gp41 has a molecular mass of 33900 Da with 312
amino acid residues. We propose that oviductin possessing
the substrate specificity of GSR simultaneously digests gp43
at Arg residues in GSR61 and GSR373 to generate the Nand
C-terminus of gp41, respectively. Dev. Genet. 25:123–