SERRATIA-MARCESCENS NUCLEASES .1. COMPARI SON OF NATURAL AND RECOMBINANT NUCLEASES BY ELECTROSPRAY MASS-SPECTROMETRY

Isoforms of the natural and recombinant nucleases of Serratia marcesce ns were characterized by their molecular mass, which was determined by electrospray mass spectrometry. The natural nuclease was isolated fro m the S. marcescens B10M1 culture, whereas the recombinant nuclease wa s obtained from Escherichia coli MT102 cells carrying plasmid p403-SD2 with the nuclease gene nuc. The primary structure for each of the iso forms isolated from the nuclease preparations was determined by compar ing its molecular mass with that of known amino acid sequence, which w as determined from the nucleotide sequence of the nuc gene. Both prepa rations included identical nuclease variants with N-terminal amino aci d residues removed. The number of isoforms in the natural nuclease was , however, significantly greater than in the recombinant nuclease. The structures of some of the isoforms were confirmed by N-terminal analy sis.