Cloning of cDNA encoding thimet oligopeptidase from Xenopus oocytes and regulation of the mRNA during oogenesis

We have isolated a cDNA clone for a zinc-requiring metallopeptidase in Xeno pus oocytes from Xenopus ovary library using oligonucleotides synthesized o n the basis of the partial amino acid sequence. The full-length 2,055 bp cD NA encodes a protein of 685 amino acid residues with a predicted molecular mass of 78,136 Da. The deduced amino acid sequence of this protein exhibits high similarity to that of human (74.1%), pig (75.3%) and rat (74.1%) thim et oligopeptidase (TOP) [EC 3.4.24.15]. Expression of the cDNA in bacterial cells resulted in the production of an active metalloenzyme. Thus, we conc luded that the metallopeptidase purified from Xenopus oocytes is a member o f the TOP family. In Northern blot analyses, one major species of Xenopus-TOP (X-TOP) mRNA of 3.0 kb was expressed relatively strongly from early stage (III) of Xenopus oogenesis, its level decreasing in later stages (V and VI). This result su ggests that the expression of X-TOP mRNA is regulated during Xenopus oogene sis.