CHARACTERIZATION OF NATURAL AND RECOMBINANT NUCLEASE ISOFORMS BY ELECTROSPRAY MASS-SPECTROMETRY

Isoforms of natural and recombinant nuclease have been characterized o n the basis of their M(r) as determined by electrospray m.s.. The natu ral nuclease was isolated and purified from Serratia marcescens B10M1 and the recombinant nuclease from Escherichia coli MT102 carrying the plasmid p403-SD2. The primary structure of each of the isoforms isolat ed from the nuclease preparations was established by comparing their m ass with the known amino acid sequence derived from the nucleotide seq uence of the nuc gene. All the preparations were found to be contamina ted with the same N-terminal split variants of native nuclease, althou gh the natural nuclease contained much larger amounts of these isoform s than did the recombinant nuclease. The structure of some of the isof orms could be verified by N-terminal sequencing, and nearly all of the m by isoelectric focusing.