Cyclin : a major maternal message in sea urchin eggs
In this thesis I describe the construction of a cDNA library of maternal mRNA from the sea-urchin Arbacia punctulata and the subsequent isolation of a cDNA clone for the cylin protein using the technique of hybrid-arrest of translation. The cyclin protein was originally identified in sea-urchin embryos as a protein that was strongly synthesised after fertilisation but destroyed at each cell division (Evans et al, 1983). The DNA sequence of the putative cyclin clone was determined. It contains an open reading frame for a protein of Mr46,000 which bears significant homology to the central region of the sequence of two other cyclin mRNAs found in eggs of the clam Spissula solidissima. The cyclin clone was subcloned into a T7 RNA polymerase transcription vector and the in vitro translation product of the encoded mRNA found to be a protein of apparent Mr56,000 on a 1-D SDS acrylamide gel, which co-migrated with the in vivo synthesised cyclin protein. When the in vitro transcript was micro-injected into Xenopus Aevis oocytes it caused germinal vesicle breakdown, indicative of entry into meiosis, suggesting a role for cyclin in the control of the cell-cycle.