Molecular cloning of cDNA encoding Xenopus laevis deoxyribonuclease I

A 1200-bp cDNA encoding Xenopus laevis deoxyribonuclease I (X. laevis DNase I) was constructed from the total RNA of a X. laevis pancreas using a rapi d amplification of cDNA ends method. When the cDNA was transiently transfec ted into COS-7 cells, the recombinant polypeptide exhibited similar enzymol ogical properties to those of the native pancreatic DNase I. The recombinan t enzyme was considerably more labile than most other vertebrate DNase I en zymes. The X. laevis DNase I polypeptide was larger than any other known ve rtebrate DNase I, containing a unique Cys-rich stretch of 68 or 70 amino ac id residues at the carboxyl terminus, and it had less well conserved bindin g sites for the Ca2+, G-actin and DNA, and two DNase I signature motifs. Th ese alterations might account for its heat instability.