Methods for the isothermal amplification of nucleic acid molecules

A method for amplifying a target polynucleotide region of a double-stranded nucleic acid molecule present in a sample, which comprises the steps:

• (A) incubating linear double-stranded nucleic acid molecules in the presence of a polymerase, nucleotides, a Cre recombinase, a primer and a restriction endonuclease;
• wherein:
• (i) each of said linear double-stranded nucleic acid molecules has two ends and comprises:
• (a) a first lox site, located at a first end of said linear molecule;
• (b) a second lox site, located at a second end of said linear molecule, wherein said first and said second lox sites are oriented with respect to one another so as to permit said Cre recombinase to mediate the circularization of said linear double-stranded molecules, and to thereby form double-stranded circular molecules;
• (c) said target polynucleotide region, located internal to said first and second lox sites;
• and
• (d) a hemi-modified restriction site, located between said target polynucleotide region and one of said lox sites, wherein one strand of said hemi-modified restriction site of each of said linear molecules contains at least one modified nucleotide residue;
• (ii) said restriction endonuclease is substantially incapable of cleaving a strand of a nucleic acid molecule that contains said modified nucleotide residue;
• (iii) said primer comprises from 3' terminus to 5' terminus:
• (a) a first polynucleotide region complementary to a 3' terminal portion of said target polynucleotide region;
• (b) a second polynucleotide region containing at least one of said modified nucleotide residues, wherein, if said second polynucleotide region were hybridized to a complementary polynucleotide, a double-stranded polynucleotide would thereby be formed that would contain one or more restriction endonuclease cleavage sites that would be recognized by said restriction endonuclease;
• (c) a third polynucleotide region, wherein, if said third polynucleotide region were hybridized to a complementary polynucleotide, a double-stranded polynucleotide would thereby be formed that would contain a lox site;
• and
• (d) a fourth polynucleotide region having a nucleotide sequence complementary to at least a portion of said third polynucleotide region, such that said third and fourth polynucleotide regions of said primer molecule are hybridizable to one another;
• and
• (iv) said incubation is conducted under conditions suitable for permitting:
• (a) said Cre recombinase to circularize said linear double-stranded nucleic acid molecules and thereby form said double-stranded circular molecules;
• (b) said restriction endonuclease to cleave one strand of said hemi-modified restriction endonuclease recognition site of said double-stranded circular molecule and thereby create an extendible 3' terminus;
• (c) said polymerase and said nucleotides to mediate template dependent extension of said extendible 3' terminus and thereby cause displacement of a single-stranded polynucleotide containing said target polynucleotide region;
• said extension further resulting in the creation of a new hemi-modified restriction recognition site;
• (d) said restriction endonuclease to cleave one strand of said newly created hemi-modified restriction endonuclease recognition site and thereby form a new extendible 3' terminus and permit the release of said single-stranded polynucleotide containing said target polynucleotide region;
• and
• (e) said primer to hybridize to said released single-stranded polynucleotide and to be extended by said polymerase and said nucleotides in a template-dependent extension to thereby form an additional copy of said linear double-stranded nucleic acid molecule;
• (B) permitting:
• said Cre recombinase-directed circularization (A)(iv)(a) of said linear molecule, said creation of said extendible 3' terminus (A)(iv)(b), said template dependent extension (A)(iv)(c), said restriction endonuclease cleavage (A)(iv)(d), and said primer hybridization (A)(iv)(e), to occur, thereby amplifying said target polynucleotide region of said double-stranded nucleic acid molecule;
• and
• (C) maintaining said incubation conditions until a desired level of amplification of said target polynucleotide region of said double-stranded nucleic acid molecule has been attained.

A method for amplifying a target polynucleotide region of a double-stranded nucleic acid molecule present in a sample, said method comprising:

• (A) incubating said sample under conditions sufficient to separate the strands of said double-stranded molecule and thereby form single-stranded nucleic acid molecules;
• (B) incubating said formed single-stranded nucleic acid molecules in the presence of first primer molecules, said first primer molecules being single-stranded nucleic acid molecules, and comprising from 3' terminus to 5' terminus:
• (1) a first polynucleotide region complementary to a 3' terminal portion of said target polynucleotide region;
• (2) a second polynucleotide region containing at least one modified nucleotide residue, wherein, if said second polynucleotide region were hybridized to a complementary polynucleotide, a double-stranded polynucleotide would thereby be formed that would contain one or more restriction endonuclease cleavage sites that would be recognized by a restriction endonuclease that is substantially incapable of cleaving a strand of a nucleic acid molecule that contains said modified nucleotide residue;
• (3) a third polynucleotide region, wherein, if said third polynucleotide region were hybridized to a complementary polynucleotide, a double-stranded polynucleotide would thereby be formed that would contain a lox site;
• and
• (4) a fourth polynucleotide region having a nucleotide sequence complementary to at least a portion of said third polynucleotide region of said first primer, such that said third and fourth polynucleotide regions of said first primer molecules are hybridizable to one another;
• and wherein said incubation is conducted in the presence of a polymerase and nucleotides lacking the modification of the modified nucleotide residue of said first primer, said incubation being under conditions sufficient to (i) permit said first polynucleotide region of said first primer molecules to hybridize to the 3' terminus of said target polynucleotide, and (ii) permit template dependent extension of said first primer molecules, to thereby form first primer extension products;
• (C) incubating said first primer extension products under conditions sufficient to separate the strands of double-stranded nucleic acid molecules and thereby produce unhybridized first primer extension products;
• (D) incubating said unhybridized first primer extension products in the presence of second primer molecules, said second primer molecules being single-stranded nucleic acid molecules, and comprising from 3' terminus to 5' terminus:
• (1) a first polynucleotide region having the sequence of a 5' terminal portion of said target polynucleotide;
• and
• (2) a second polynucleotide region, wherein, if said second polynucleotide region were hybridized to a complementary polynucleotide, a double-stranded polynucleotide would thereby be formed that would contain a lox site;
• wherein said incubation is conducted in the presence of a polymerase and nucleotides lacking the modification of the modified nucleotides present in said first primer, said incubation being under conditions sufficient to permit (i) said unhybridized first primer extension products to hybridize to the 3' terminus of said second primer molecules, and (ii) template dependent extension of said first primer extension products, and of said second primer molecules, to thereby form linear double-stranded nucleic acid molecules having a lox site at each end, and containing said target polynucleotide that is to be amplified and a hemi-modified restriction site;
• (E) incubating the linear double-stranded nucleic acid molecules of step (D) in the presence of Cre recombinase, said restriction endonuclease, said polymerase and said nucleotides lacking the modification of the modified nucleotide residue of said first primer;
• wherein said incubation permits the following reactions to occur:
• (1) said Cre recombinase to circularize said linear double-stranded nucleic acid molecules having a lox site at each end, to thereby form a double-stranded circular molecule;
• (2) said restriction endonuclease to cleave a non-modified nucleotide-containing strand of said hemi-modified restriction endonuclease recognition site of said double-stranded circular molecule to thereby form an extendible 3' terminus;
• (3) said polymerase and said non-modified nucleotides to mediate template-dependent primer extension of said extendible 3' terminus to thereby cause displacement of a single-stranded polynucleotide containing said target polynucleotide region;
• said primer extension further resulting in the creation of a new hemi-modified restriction recognition site;
• and
• (4) said restriction endonuclease to cleave a non-modified nucleotide-containing strand of said newly created hemi-modified restriction endonuclease recognition site to thereby form a new extendible 3' terminus, and permit the release of said single-stranded polynucleotide containing said target polynucleotide region, wherein said displacement and said release accomplishes an amplification of said target polynucleotide;
• and
• (F) maintaining said incubation conditions of step (E) until a desired level of amplification of said target polynucleotide has been attained.

A method for amplifying a target polynucleotide region of a double-stranded nucleic acid molecule present in a sample, said method comprising:

• (A) incubating said sample under conditions sufficient to separate the strands of said double-stranded molecule and thereby form single-stranded nucleic acid molecules;
• (B) incubating said formed single-stranded nucleic acid molecules in the presence of first primer molecules, said first primer molecules being single-stranded nucleic acid molecules, and comprising from 3' terminus to 5' terminus:
• (1) a first polynucleotide region complementary to a 3' terminal portion of said target polynucleotide region;
• (2) a second polynucleotide region containing at least one modified nucleotide residue, wherein, if said second polynucleotide region were hybridized to a complementary polynucleotide, a double-stranded polynucleotide would thereby be formed that would contain one or more restriction endonuclease cleavage sites that would be recognized by a restriction endonuclease that is substantially incapable of cleaving a strand of a nucleic acid molecule that contains said modified nucleotide residue;
• and
• (3) a third polynucleotide region, wherein, if said third polynucleotide region were hybridized to a complementary polynucleotide, a double-stranded polynucleotide would thereby be formed that would contain a lox site;
• wherein said incubation is conducted in the presence of a polymerase and nucleotides lacking the modification of the modified nucleotide residue of said first primer, said incubation being under conditions sufficient to (i) permit said first polynucleotide region of said first primer molecules to hybridize to the 3' terminus of said target polynucleotide, and (ii) permit template dependent extension of said first primer molecules, to thereby form first primer extension products;
• (C) incubating said first primer extension products under conditions sufficient to separate the strands of double-stranded nucleic acid molecules and thereby produce unhybridized first primer extension products;
• (D) incubating said unhybridized first primer extension products in the presence of second primer molecules, said second primer molecules being single-stranded nucleic acid molecules, and comprising from 3' terminus to 5' terminus:
• (1) a first polynucleotide region having the sequence of a 5' terminal portion of said target polynucleotide;
• (2) a second polynucleotide region, wherein, if said second polynucleotide region were hybridized to a complementary polynucleotide, a double-stranded polynucleotide would thereby be formed that would contain a lox site;
• and
• (3) a third polynucleotide region having a nucleotide sequence complementary to at least a portion of said second polynucleotide region, such that said second and third polynucleotide regions of said second primer molecules are hybridizable to one another;
• and
• wherein said incubation is conducted in the presence of a polymerase and nucleotides lacking the modification of the modified nucleotides present in said first primer, said incubation being under conditions sufficient to permit (i)said unhybridized first primer extension products to hybridize to the 3' terminus of said second primer molecules, and (ii) template dependent extension of said first primer extension products, and of said second primer molecules, to thereby form linear double-stranded nucleic acid molecules having a lox site at each end, and containing said target polynucleotide that is to be amplified and a hemi-modified restriction site;
• (E) incubating the linear double-stranded nucleic acid molecules of step (D) in the presence of Cre recombinase, said restriction endonuclease, said polymerase and said nucleotides lacking the modification of the modified nucleotide residue of said first primer;
• wherein said incubation permits the following reactions to occur:
• (1) said Cre recombinase to circularize said linear double-stranded nucleic acid molecules having a lox site at each end, to thereby form a double-stranded circular molecule;
• (2) said restriction endonuclease to cleave a non-modified nucleotide-containing strand of said hemi-modified restriction endonuclease recognition site of said double-stranded circular molecule to thereby form an extendible 3' terminus;
• (3) said polymerase and said non-modified nucleotides to mediate template-dependent primer extension of said extendible 3' terminus to thereby cause displacement of a single-stranded polynucleotide containing said target polynucleotide region;
• said primer extension further resulting in the creation of a new hemi-modified restriction recognition site;
• and
• (4) said restriction endonuclease to cleave a non-modified nucleotide-containing strand of said newly created hemi-modified restriction endonuclease recognition site to thereby form a new extendible 3' terminus, and permit the release of said single-stranded polynucleotide containing said target polynucleotide region, wherein said displacement and said release accomplishes an amplification of said target polynucleotide;
• and
• (F) maintaining said incubation conditions of step (E) until a desired level of amplification of said target polynucleotide has been attained.