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Dev Growth Differ
2003 Jun 01;453:283-94. doi: 10.1046/j.1524-4725.2003.696.x.
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Mr 25 000 protein, a substrate for protein serine/threonine kinases, is identified as a part of Xenopus laevis vitellogenin B1.
A phosphorylated protein with a molecular mass of 25 000 (pp25) previously purified from the cytosolic fraction of Xenopus laevis oocytes is an effective phosphate acceptor for casein kinases and protein kinase C. In this study, based on the partial amino acid sequence of pp25, a cDNA was isolated that encodes a new yolk precursor protein, Xenopus vitellogenin B1, which contained the sequence encoding pp25. Both mRNA and protein of vitellogenin B1 were expressed in all of the female organs examined. In agreement with a previous report, the amount of vitellogenin B1 protein in the liver increased after stimulation with estrogen. These results suggest that pp25 is a cytosolic non-crystallized yolk protein nutrient source, but it might also play a role in rapid development.
Separation of peptides derived from dephosphorylated
pp25 by reverse-phase high performance liquid chromatography
(HPLC). Solid and dotted lines show absorbance at
214 nm and concentration of acetonitrile, respectively.
Fig. 2. Nucleotide and deduced
amino acid sequences of pp25
precursor protein. The putative
pp25 region is boxed. The serine
clusters (Ser Clu), the aminoterminal
amino acid sequence
reported previously (Hashimoto
et al. 1995, 1996) and in Table 1
(N-ter seq), partial amino acid
sequences (Pep; Table 1), and
amino terminus of lipovitellin 2
(Montorzi et al. 1995) are all
indicated by solid underlines. The
nucleotide sequence data have
been deposited in DDBJ/EMBL/
GenBank (accession number
AB092605). This figure is continued
on pages 287–290.
Fig. 3. Sequence analysis of
Xenopus vitellogenin B1. (a)
Comparison of the predicted
amino acid sequence of Xenopus
vitellogenin B1 (pp25 pre) with
that of chicken (Gg) vitellogenin II
(Yamamura et al. 1995) and
Xenopus vitellogenin A2 (Wallace
et al. 1990; Plowman et al. 1994;
Sunderman et al. 1995). Sequence
homology (expressed as
percentage identity) was determined
by using the DNASIS
program for each of the four
putative yolk protein regions. LV,
lipovitellin; PV, phosvitin; VTG,
vitellogenin; YGP, york glycoprotein;
pp25 pre, pp25 precursor;
Xl, Xenopus laevis. (b)
Comparison of the nucleotide
sequence of Xenopus vitellogenin
B1 (pp25 pre) with those of partial
vitellogenin B1 and B2 sequences
(Gerber-Huber et al. 1987;
Plowman et al. 1994). Nucleotide
sequences identical to those of
Xenopus vitellogenin B1 are
indicated by (:).
Fig. 4. Tissue-specific expression of Xenopus vitellogenin B1.
(a) Tissue-specific expression of the mRNA of Xenopus vitellogenin
B1 and the housekeeping protein gene Xenopus GAPDH.
Xenopus vitellogenin B1 and Xenopus GAPDH transcripts from
various tissues of female Xenopus adults were analyzed by
reverse transcription (RT)–polymerase chain reaction (PCR). (b)
The expression of the mRNA of Xenopus vitellogenin B1 in both
the ovary and the lung were detected by nested PCR. (c) Organ
western blot analysis of Xenopus vitellogenin B1. A sample of
protein (20 μg from stomach, kidney and ovary; 26 μg from
heart; 30 μg from lung; and 40 μg from liver) from various tissues
of female Xenopus adults was analyzed by western blotting by
using the antipp25 antibody. The arrow on the right shows the
putative position of vitellogenin B1 with molecular mass of
approximately 220 000. Numbers on the left indicate the
positions of molecular mass markers in kDa: 212, myosin; 170,
2-macroglobulin. (d) Induction of putative vitellogenin B1 in the
liver of Xenopus treated with estrogen. A sample of liver protein
(25 μg) from an untreated Xenopus female or one injected with
17-estradiol 2 weeks before analysis by western blotting by
using the antipp25 antibody.