Cyclin B cDNA was cloned from the ovary of the starfish Asterina pectinifer
a and analyzed by RT-PCR and 3 '- and 5 ' -RACE techniques. The cDNA consis
ts of a 0.13-kb upstream untranslated region, a 1.22-kb coding region, and
a 0.86-kb downstream untranslated region. The open reading frame encoded a
polypeptide of 404 amino acid residues with a calculated molecular weight o
f 45,692, All the characteristic sequences, such as destruction and cyclin
boxes, cyclin B motif, and cytoplasmic retention and nuclear export signals
, were found in the newly cloned cyclin B cDNA, The deduced amino acid sequ
ence of the cyclin B cDNA was highly homologous in the middle and carboxy t
erminal regions to that from mature eggs of the same organism, but quite di
fferent in the amino terminal region, Evidence was obtained which suggested
that this cyclin B is expressed in immature and maturing oocytes and is th
e same as that cloned from mature eggs.