| Abstract: | A nuclease with novel activities has been isolated and purifiedto apparent homogeneity from pea chloroplasts. The enzyme preferssingle-stranded (ss) circular DNA; its activity being 1500-foldhigher with the ss circular DNA than with the linear double-strandedDNA substrates. The single-stranded DNase activity is stableat moderately high temperature (50 C) and inhibited in thepresence of 75 mM NaCl. It binds negatively supercoiled DNAin the stoichiometric fashion, but behaves catalytically onthe single-stranded circular DNA. Although the DNase activitydoes not recognize any specific nucleotide sequence, the co-operativemode of activity seems to be a novel one. The protein is a monomerof 35 kDa and binds with DNA predominantly through electrostaticinteractions. The drug distamycin blocks the endonuclease activitysuggesting that the protein binds at the minor groove of DNA.A RNase activity has also been found associated with the ss-DNAendonuclease. Key words: Pea, chloroplast, endonuclease |
