Search tips
Search criteria

Results 1-2 (2)

Clipboard (0)
Year of Publication
Document Types
1.  Related bifunctional restriction endonuclease-methyltransferase triplets: TspDTI, Tth111II/TthHB27I and TsoI with distinct specificities 
BMC Molecular Biology  2012;13:13.
We previously defined a family of restriction endonucleases (REases) from Thermus sp., which share common biochemical and biophysical features, such as the fusion of both the nuclease and methyltransferase (MTase) activities in a single polypeptide, cleavage at a distance from the recognition site, large molecular size, modulation of activity by S-adenosylmethionine (SAM), and incomplete cleavage of the substrate DNA. Members include related thermophilic REases with five distinct specificities: TspGWI, TaqII, Tth111II/TthHB27I, TspDTI and TsoI.
TspDTI, TsoI and isoschizomers Tth111II/TthHB27I recognize different, but related sequences: 5'-ATGAA-3', 5'-TARCCA-3' and 5'-CAARCA-3' respectively. Their amino acid sequences are similar, which is unusual among REases of different specificity. To gain insight into this group of REases, TspDTI, the prototype member of the Thermus sp. enzyme family, was cloned and characterized using a recently developed method for partially cleaving REases.
TspDTI, TsoI and isoschizomers Tth111II/TthHB27I are closely related bifunctional enzymes. They comprise a tandem arrangement of Type I-like domains, like other Type IIC enzymes (those with a fusion of a REase and MTase domains), e.g. TspGWI, TaqII and MmeI, but their sequences are only remotely similar to these previously characterized enzymes. The characterization of TspDTI, a prototype member of this group, extends our understanding of sequence-function relationships among multifunctional restriction-modification enzymes.
PMCID: PMC3384240  PMID: 22489904
2.  Cloning and analysis of a bifunctional methyltransferase/restriction endonuclease TspGWI, the prototype of a Thermus sp. enzyme family 
BMC Molecular Biology  2009;10:52.
Restriction-modification systems are a diverse class of enzymes. They are classified into four major types: I, II, III and IV. We have previously proposed the existence of a Thermus sp. enzyme family, which belongs to type II restriction endonucleases (REases), however, it features also some characteristics of types I and III. Members include related thermophilic endonucleases: TspGWI, TaqII, TspDTI, and Tth111II.
Here we describe cloning, mutagenesis and analysis of the prototype TspGWI enzyme that recognises the 5'-ACGGA-3' site and cleaves 11/9 nt downstream. We cloned, expressed, and mutagenised the tspgwi gene and investigated the properties of its product, the bifunctional TspGWI restriction/modification enzyme. Since TspGWI does not cleave DNA completely, a cloning method was devised, based on amino acid sequencing of internal proteolytic fragments. The deduced amino acid sequence of the enzyme shares significant sequence similarity with another representative of the Thermus sp. family – TaqII. Interestingly, these enzymes recognise similar, yet different sequences in the DNA. Both enzymes cleave DNA at the same distance, but differ in their ability to cleave single sites and in the requirement of S-adenosylmethionine as an allosteric activator for cleavage. Both the restriction endonuclease (REase) and methyltransferase (MTase) activities of wild type (wt) TspGWI (either recombinant or isolated from Thermus sp.) are dependent on the presence of divalent cations.
TspGWI is a bifunctional protein comprising a tandem arrangement of Type I-like domains; particularly noticeable is the central HsdM-like module comprising a helical domain and a highly conserved S-adenosylmethionine-binding/catalytic MTase domain, containing DPAVGTG and NPPY motifs. TspGWI also possesses an N-terminal PD-(D/E)XK nuclease domain related to the corresponding domains in HsdR subunits, but lacks the ATP-dependent translocase module of the HsdR subunit and the additional domains that are involved in subunit-subunit interactions in Type I systems. The MTase and REase activities of TspGWI are autonomous and can be uncoupled. Structurally and functionally, the TspGWI protomer appears to be a streamlined 'half' of a Type I enzyme.
PMCID: PMC2700111  PMID: 19480701

Results 1-2 (2)