Isolation of SagI, a new HaeIII isoschizomer from Streptococcus agalactiae

Biochemical and molecular characterization of a restriction endonuclease Tvu2HI from Thermoactinomyces vulgaris 2H and study of its R-M system

A bacterial strain 2H isolated from soil and identified as Thermoactinomyces vulgaris produce a potent Type II restriction endonuclease activity that has been extracted by a PEG/dextran aqueous two-phase system. Optimal temperature for the restriction endonuclease activity was 55-65°C. Specific DNA cleavage was obtained at pH range 7-10 and 10-20mM MgCl₂. Restriction cleavage analysis followed by sequencing confirms GG^CC as the recognition sequence. This enzyme, named Tvu2HI, is a thermostable isoschizomer of the mesophilic prototype restriction endonuclease HaeIII. Sequencing of the complete Thermoactinomyces vulgaris 2H genome revealed the presence of two adjacent ORFs coding for the restriction endonuclease Tvu2HI and the corresponding methyltransferase; an ORF coding for a putative Vsr nicking enzyme was found close to those coding for the Tvu2HI restriction-modification system. Phylogenetic analysis based on sequence alignment suggests a common origin of Tvu2HI R-M system with HaeIII-like R-M systems. This is the first investigation dealing with a Type II restriction endonuclease identified in a natural isolate of the genus Thermoactinomyces.

Isolation and characterization of a newly identified type II restriction endonuclease from a local Streptomyces sp. in Taiwan

Streptomyces chusanensis ZS-2, isolated from a soil sample in Chusan in Taiwan, was found to produce a new Type II restriction endonuclease. This restriction enzyme was designated as SchI. The purified enzyme was characterized as having a subunit mol wt of 28 kDa, and was apparently free from exonuclease activities. It cleaves the phosphodiester bond between the fourth C and the fifth G on the 5'-CCGCGG-3' sequence of DNAs, leaving a 2-nucleotide protruding end at its 3' site. This data suggests that SchI is an isoschizomer of SacII. In addition, based on the comparison between SchI and SacII regarding reaction parameters, it seems that SchI is a better choice of restriction enzyme for genetic analysis and mapping.