A novel endonuclease from kinetoplastid hemoflagellated protozoan parasiteLeishmania

A nuclease activity has been purified from the nuclei-kinetoplast fraction of Leishmania, This enzyme, termed endonuclease M (Endo M), is shown by ele ctrophoresis in a denaturing polyacrylamide gel to be associated with a sin gle polypeptide of molecular mass 52 kDa, Physical analysis of the enzyme i ndicates that it has a sedimentation coefficient S-20,S-W, of 4.5S, a Stoke 's radius of 32.5 Angstrom, and a native molecular mass of 53 kDa, The fina l Mono Q purified Endo M possesses both DNase and RNase activities. It acts as an endonuclease by introducing random single-stranded nicks into the su percoiled DNA molecules, that often leads to its linearization due to nicki ng at the opposite strands, and subsequent degradation of the DNA with furt her incubation, Single-stranded DNA is twice preferred to double-stranded D NA as substrate. Single-stranded RNA is also degraded rapidly and is compet itive as a substrate with single-stranded DNA, RNA:DNA hybrids, however, ar e largely resistant to the Endo M digestion.