The phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS), a major carbohydrate active-transport system, catalyses the phosphorylation of incoming sugar substrates concomitant with their translocation across the cell membrane.This family represents the IIC component of the PTS galactitol-specific family. Gat family PTS systems typically have 3 components: IIA, IIB and IIC [].
The binding of the negative modulator of initiation of replication (SeqA) protein to hemimethylated GATC sequences is important in the negative modulation of chromosomal initiation at oriC, and in the formation of SeqA foci necessary for Escherichia coli chromosome segregation []. SeqA tetramers are able to aggregate or multimerize in a reversible, concentration-dependent manner []. Apart from its function in the control of DNA replication, SeqA may also be a specific transcription factor [].The C-terminal domain binds DNA, binding to hemimethylated GATC sequences at oriC [, ]. The structure of the C-terminal domain consists of seven α-helices and three-stranded β-sheet.
The binding of the negative modulator of initiation of replication (SeqA) protein to hemimethylated GATC sequences is important in the negative modulation of chromosomal initiation at oriC, and in the formation of SeqA foci necessary for Escherichia coli chromosome segregation []. SeqA tetramers are able to aggregate or multimerize in a reversible, concentration-dependent manner []. Apart from its function in the control of DNA replication, SeqA may also be a specific transcription factor [].The C-terminal domain binds DNA, binding to hemimethylated GATC sequences at oriC [, ]. The structure of the C-terminal domain consists of seven α-helices and three-stranded β-sheet.
This entry represents a family related to GatC, the third subunit of an enzyme for completing the charging of tRNA(Gln) by amidating the Glu-tRNA(Gln). The few known archaea that contain a member of this family appear to produce Asn-tRNA(Asn) by an analogous amidotransferase reaction. This protein is proposed to substitute for GatC in the charging of both tRNAs.
The binding of the negative modulator of initiation of replication (SeqA) protein to hemimethylated GATC sequences is important in the negative modulation of chromosomal initiation at oriC, and in the formation of SeqA foci necessary for Escherichia coli chromosome segregation []. SeqA tetramers are able to aggregate or multimerize in a reversible, concentration-dependent manner []. Apart from its function in the control of DNA replication, SeqA may also be a specific transcription factor [].
The binding of SeqA protein to hemimethylated GATC sequences is important in the negative modulation of chromosomal initiation at oriC, and in the formation of SeqA foci necessary for Escherichia coli chromosome segregation []. SeqA tetramers are able to aggregate or multimerise in a reversible, concentration-dependent manner []. Apart from its function in the control of DNA replication, SeqA may also be a specific transcription factor [].This family represents the N-terminal domain of SeqA: a short domain that is reported to mediate the dimerisation of SeqA [].
In prokaryotes, the major role of DNA methylation is to protect host DNA against degradation by restriction enzymes. There are 2 major classes of DNA methyltransferase that differ in the nature of the modifications they effect. The members of one class (C-MTases) methylate a ring carbon and form C5-methylcytosine (see ). Members of the second class (N-MTases) methylate exocyclic nitrogens and form either N4-methylcytosine(N4-MTases) or N6-methyladenine (N6-MTases). Both classes of MTase utilise the cofactor S-adenosyl-L-methionine (SAM) as the methyl donor and are active as monomeric enzymes [].N-6 adenine-specific DNA methylases () (A-Mtase) are enzymes that specifically methylate the amino group at the C-6 position of adenines in DNA. They include enzymes are found in bacterial restriction-modification systems, as well as solitary enzymes that do not have a restriction enzyme counterpart [].Proteins in this entry are homologous to Dam methyltransferase () from Escherichia coli which recognises the sequence GATC and methylates the adenine moeity. This protein is not part of a restriction modification system and its activity influences cellular functions such as gene transcription, DNA mismatch repair, initiation of chromosome replication and nucleoid structure []. It is dispensible in E. coli, but has been shown to be required for viability in Yersinia and Vibrio species, virulence in Salmonella, and replication in some bacteriophages. Dam methyltransferase consists of a seven-stranded beta sheet sandwiched between two layers of alpha helices [, ]. The beta sheet contains the catalytic domain, while the target recognition domain is composed of five alpha helices and a beta hairpin. The methyl donor binds to a region of the beta sheet, surrounded by conserved residues, which is next to a narrow surface pocket thought to contain the active site.
There are four classes of restriction endonucleases: types I, II,III and IV. All types of enzymes recognise specific short DNA sequences and carry out the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. They differ in their recognition sequence, subunit composition, cleavage position, and cofactor requirements [, ], as summarised below:Type I enzymes () cleave at sites remote from recognition site; require both ATP and S-adenosyl-L-methionine to function; multifunctional protein with both restriction and methylase () activities.Type II enzymes () cleave within or at short specific distances from recognition site; most require magnesium; single function (restriction) enzymes independent of methylase.Type III enzymes () cleave at sites a short distance from recognition site; require ATP (but doesn't hydrolyse it); S-adenosyl-L-methionine stimulates reaction but is not required; exists as part of a complex with a modification methylase methylase ().Type IV enzymes target methylated DNA.Type II restriction endonucleases () are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. These site-specific deoxyribonucleases catalyse the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. Of the 3000 restriction endonucleases that have been characterised, most are homodimeric or tetrameric enzymes that cleave target DNA at sequence-specific sites close to the recognition site. For homodimeric enzymes, the recognition site is usually a palindromic sequence 4-8 bp in length. Most enzymes require magnesium ions as a cofactor for catalysis. Although they can vary in their mode of recognition, many restriction endonucleases share a similar structural core comprising four β-strands and one α-helix, as well as a similar mechanism of cleavage, suggesting a common ancestral origin []. However, there is still considerable diversity amongst restriction endonucleases [, ]. The target site recognition process triggers large conformational changes of the enzyme and the target DNA, leading to the activation of the catalytic centres. Like other DNA binding proteins, restriction enzymes are capable of non-specific DNA binding as well, which is the prerequisite for efficient target site location by facilitated diffusion. Non-specific binding usually does not involve interactions with the bases but only with the DNA backbone []. This entry is found in type II restriction enzymes such as DpnII (), which recognises the double-stranded unmethylated sequence GATC and cleave before G-1 [], where it encompasess the full length of the protein. It is also found in a number of proteins of unknown function, where it is located adjacent to a DNA adenine-specific methyltransferase domain ().
There are four classes of restriction endonucleases: types I, II,III and IV. All types of enzymes recognise specific short DNA sequences and carry out the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. They differ in their recognition sequence, subunit composition, cleavage position, and cofactor requirements [, ], as summarised below:Type I enzymes () cleave at sites remote from recognition site; require both ATP and S-adenosyl-L-methionine to function; multifunctional protein with both restriction and methylase () activities.Type II enzymes () cleave within or at short specific distances from recognition site; most require magnesium; single function (restriction) enzymes independent of methylase.Type III enzymes () cleave at sites a short distance from recognition site; require ATP (but doesn't hydrolyse it); S-adenosyl-L-methionine stimulates reaction but is not required; exists as part of a complex with a modification methylase methylase ().Type IV enzymes target methylated DNA.Type II restriction endonucleases () are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. These site-specific deoxyribonucleases catalyse the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. Of the 3000 restriction endonucleases that have been characterised, most are homodimeric or tetrameric enzymes that cleave target DNA at sequence-specific sites close to the recognition site. For homodimeric enzymes, the recognition site is usually a palindromic sequence 4-8 bp in length. Most enzymes require magnesium ions as a cofactor for catalysis. Although they can vary in their mode of recognition, many restriction endonucleases share a similar structural core comprising four β-strands and one α-helix, as well as a similar mechanism of cleavage, suggesting a common ancestral origin []. However, there is still considerable diversity amongst restriction endonucleases [, ]. The target site recognition process triggers large conformational changes of the enzyme and the target DNA, leading to the activation of the catalytic centres. Like other DNA binding proteins, restriction enzymes are capable of non-specific DNA binding as well, which is the prerequisite for efficient target site location by facilitated diffusion. Non-specific binding usually does not involve interactions with the bases but only with the DNA backbone []. This entry represents type II restriction enzymes such as DpnII (), which recognises the double-stranded unmethylated sequence GATC and cleave before G-1 [].
There are four classes of restriction endonucleases: types I, II,III and IV. All types of enzymes recognise specific short DNA sequences and carry out the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. They differ in their recognition sequence, subunit composition, cleavage position, and cofactor requirements [, ], as summarised below:Type I enzymes () cleave at sites remote from recognition site; require both ATP and S-adenosyl-L-methionine to function; multifunctional protein with both restriction and methylase () activities.Type II enzymes () cleave within or at short specific distances from recognition site; most require magnesium; single function (restriction) enzymes independent of methylase.Type III enzymes () cleave at sites a short distance from recognition site; require ATP (but doesn't hydrolyse it); S-adenosyl-L-methionine stimulates reaction but is not required; exists as part of a complex with a modification methylase methylase ().Type IV enzymes target methylated DNA.Type II restriction endonucleases () are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. These site-specific deoxyribonucleases catalyse the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. Of the 3000 restriction endonucleases that have been characterised, most are homodimeric or tetrameric enzymes that cleave target DNA at sequence-specific sites close to the recognition site. For homodimeric enzymes, the recognition site is usually a palindromic sequence 4-8 bp in length. Most enzymes require magnesium ions as a cofactor for catalysis. Although they can vary in their mode of recognition, many restriction endonucleases share a similar structural core comprising four β-strands and one α-helix, as well as a similar mechanism of cleavage, suggesting a common ancestral origin []. However, there is still considerable diversity amongst restriction endonucleases [, ]. The target site recognition process triggers large conformational changes of the enzyme and the target DNA, leading to the activation of the catalytic centres. Like other DNA binding proteins, restriction enzymes are capable of non-specific DNA binding as well, which is the prerequisite for efficient target site location by facilitated diffusion. Non-specific binding usually does not involve interactions with the bases but only with the DNA backbone []. This entry represents restriction endonucleases EcoRV, NaeI, HincII, and Sau3AI, as well as the DNA mismatch repair protein MutH, which are closely related in sequence and structure. EcoRV recognises the DNA sequence GATATC and cleaves after T-1 [], NaeI recognises GCCGCC and cleaves after C-2 [], HincII recognises GTYRAC and cleaves after the pyrimidine Y [], and Sau3AI recognises GATC and cleaves prior to G-1 [].MutH, along with MutS and MutL, is essential for initiation of methyl-directed DNA mismatch repair to correct mistakes made during DNA replication in Escherichia coli. MutH cleaves a newly synthesized and unmethylated daughter strand 5' to the sequence d(GATC) in a hemi-methylated duplex. Activation of MutH requires the recognition of a DNA mismatch by MutS and MutL. With sequence homology to Sau3AI and structural similarity to PvuII endonuclease, MutH shows sequence and structural similarity with PvuII and Sau3AI, indicating a strong relationship with these enzymes through divergent evolution, suggesting that type II restriction endonucleases evolved from a common ancestor [].
There are four classes of restriction endonucleases: types I, II,III and IV. All types of enzymes recognise specific short DNA sequences and carry out the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. They differ in their recognition sequence, subunit composition, cleavage position, and cofactor requirements [, ], as summarised below:Type I enzymes () cleave at sites remote from recognition site; require both ATP and S-adenosyl-L-methionine to function; multifunctional protein with both restriction and methylase () activities.Type II enzymes () cleave within or at short specific distances from recognition site; most require magnesium; single function (restriction) enzymes independent of methylase.Type III enzymes () cleave at sites a short distance from recognition site; require ATP (but doesn't hydrolyse it); S-adenosyl-L-methionine stimulates reaction but is not required; exists as part of a complex with a modification methylase methylase ().Type IV enzymes target methylated DNA.Type II restriction endonucleases () are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. These site-specific deoxyribonucleases catalyse the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. Of the 3000 restriction endonucleases that have been characterised, most are homodimeric or tetrameric enzymes that cleave target DNA at sequence-specific sites close to the recognition site. For homodimeric enzymes, the recognition site is usually a palindromic sequence 4-8 bp in length. Most enzymes require magnesium ions as a cofactor for catalysis. Although they can vary in their mode of recognition, many restriction endonucleases share a similar structural core comprising four β-strands and one α-helix, as well as a similar mechanism of cleavage, suggesting a common ancestral origin []. However, there is still considerable diversity amongst restriction endonucleases [, ]. The target site recognition process triggers large conformational changes of the enzyme and the target DNA, leading to the activation of the catalytic centres. Like other DNA binding proteins, restriction enzymes are capable of non-specific DNA binding as well, which is the prerequisite for efficient target site location by facilitated diffusion. Non-specific binding usually does not involve interactions with the bases but only with the DNA backbone []. This entry includes the restriction endonuclease Sau3AI and the DNA mismatch repair protein MutH, which are closely related in sequence and structure. Sau3AI recognises GATC and cleaves prior to G-1 [].MutH, along with MutS and MutL, is essential for initiation of methyl-directed DNA mismatch repair to correct mistakes made during DNA replication in Escherichia coli. MutH cleaves a newly synthesized and unmethylated daughter strand 5' to the sequence d(GATC) in a hemi-methylated duplex. Activation of MutH requires the recognition of a DNA mismatch by MutS and MutL. With sequence homology to Sau3AI and structural similarity to PvuII endonuclease, MutH shows sequence and structural similarity with PvuII and Sau3AI, indicating a strong relationship with these enzymes through divergent evolution, suggesting that type II restriction endonucleases evolved from a common ancestor [].
