Signal boost cascade assay
The present disclosure relates to compositions of matter and assay methods used to detect one or more target nucleic acids of interest in a sample. The compositions and methods provide signal boost upon detection of target nucleic acids of interest in less than one minute and in some instances instantaneously at ambient temperatures down to 16° C. or less, without amplification of the target nucleic acids yet allowing for massive multiplexing, high accuracy and minimal non-specific signal generation.
1 . A method for preventing unwinding of blocked nucleic acid molecules in the presence of an RNP comprising the steps of:
providing blocked nucleic acid molecules;
providing ribonucleoprotein complexes comprising a Cas12a nucleic acid-guided nuclease that exhibits both cis- and trans-cleavage activity upon activation and a gRNA that recognizes an unblocked nucleic acid molecule resulting from trans-cleavage of the blocked nucleic acid molecules; and
engineering the Cas 12a nucleic acid-guided nuclease to comprise at least one mutation to domains that interact with the PAM region or surrounding sequences on the blocked nucleic acid molecule to result in a variant nucleic acid-guided nuclease where single stranded DNA is cleaved faster than double stranded DNA is cleaved.
2 . The method of claim 1 , wherein the blocked nucleic acid molecules comprise a structure represented by any one of Formulas I-IV, wherein Formulas I-IV are in the 5′-to-3′ direction:
(a) A-(B-L) J -C-M-T-D (Formula I);
wherein A is 0-15 nucleotides in length;
B is 4-12 nucleotides in length;
L is 3-25 nucleotides in length;
J is an integer between 1 and 10;
C is 4-15 nucleotides in length;
M is 1-25 nucleotides in length or is absent, wherein if M is absent then A-(B-L) J -C and T-D are separate nucleic acid strands;
T is 17-135 nucleotides in length and comprises at least 50% sequence complementarity to B and C; and
D is 0-10 nucleotides in length and comprises at least 50% sequence complementarity to A;
(b) D-T-T′-C-(L-B) J -A (Formula II);
wherein D is 0-10 nucleotides in length;
T-T′ is 17-135 nucleotides in length;
T′ is 1-10 nucleotides in length and does not hybridize with T;
C is 4-15 nucleotides in length and comprises at least 50% sequence complementarity to T;
L is 3-25 nucleotides in length and does not hybridize with T;
B is 4-12 nucleotides in length and comprises at least 50% sequence complementarity to T;
J is an integer between 1 and 10;
A is 0-15 nucleotides in length and comprises at least 50% sequence complementarity to D;
(c) T-D-M-A-(B-L) J -C (Formula III);
wherein T is 17-135 nucleotides in length;
D is 0-10 nucleotides in length;
M is 1-25 nucleotides in length or is absent, wherein if M is absent then T-D and A-(B-L) J -C are separate nucleic acid strands;
A is 0-15 nucleotides in length and comprises at least 50% sequence complementarity to D;
B is 4-12 nucleotides in length and comprises at least 50% sequence complementarity to T;
L is 3-25 nucleotides in length;
J is an integer between 1 and 10; and
C is 4-15 nucleotides in length; or
(d) T-D-M-A-L p -C (Formula IV);
wherein T is 17-31 nucleotides in length (e.g., 17-100, 17-50, or 17-25);
D is 0-15 nucleotides in length;
M is 1-25 nucleotides in length;
A is 0-15 nucleotides in length and comprises a sequence complementary to D; and
L is 3-25 nucleotides in length;
p is 0 or 1;
C is 4-15 nucleotides in length and comprises a sequence complementary to T.
3 . The method of claim 2 , wherein:
(a) T of Formula I comprises at least 80% sequence complementarity to B and C;
(b) D of Formula I comprises at least 80% sequence complementarity to A;
(c) C of Formula II comprises at least 80% sequence complementarity to T;
(d) B of Formula II comprises at least 80% sequence complementarity to T;
(e) A of Formula II comprises at least 80% sequence complementarity to D;
(f) A of Formula III comprises at least 80% sequence complementarity to D;
(g) B of Formular III comprises at least 80% sequence complementarity to T;
(h) A of Formula IV comprises at least 80% sequence complementarity to D; and/or
(i) C of Formula IV comprises at least 80% sequence complementarity to T.
4 . The method of claim 1 , wherein the Cas12a nucleic acid-guided nuclease comprises a mutation selected from mutations to amino acid residues K548, N552 and K607 in relation to SEQ ID NO: 2.
5 . The method of claim 4 , wherein the Cas 12a nucleic acid-guided nuclease comprises at least two mutations selected from mutations to amino acid residues K548, N552 and K607 in relation to SEQ ID NO:2.
6 . The method of claim 5 , wherein the Cas12a nucleic acid-guided nuclease comprises mutations to amino acid residues K548, N552 and K607 in relation to SEQ ID NO:2.
7 . The method of claim 1 , wherein the Cas12a nucleic acid-guided nuclease comprises a mutation selected from mutations to amino acid residues K534, Y538 and R591 in relation to SEQ ID NO: 3.
8 . The method of claim 7 , wherein the Cas12a nucleic acid-guided nuclease comprises at least two mutations selected from mutations to amino acid residues K534, Y538 and R591 in relation to SEQ ID NO:3.
9 . The method of claim 8 , wherein the Cas12a nucleic acid-guided nuclease comprises mutations to amino acid residues K534, Y538 and R591 in relation to SEQ ID NO:3.
10 . The method of claim 1 , wherein the Cas12a nucleic acid-guided nuclease comprises a mutation selected from mutations to amino acid residues K541, N545 and K601 in relation to SEQ ID NO: 4.
11 . The method of claim 10 , wherein the Cas 12a nucleic acid-guided nuclease comprises at least two mutations selected from mutations to amino acid residues K541, N545 and K601 in relation to SEQ ID NO:4.
12 . The method of claim 11 , wherein the Cas12a nucleic acid-guided nuclease comprises mutations to amino acid residues K541, N545 and K601 in relation to SEQ ID NO:4.
13 . The method of claim 1 , wherein the Cas12a nucleic acid-guided nuclease comprises a mutation selected from mutations to amino acid residues K579, N583 and K635 in relation to SEQ ID NO: 5.
14 . The method of claim 13 , wherein the Cas 12a nucleic acid-guided nuclease comprises at least two mutations selected from mutations to amino acid residues K579, N583 and K635 in relation to SEQ ID NO:5.
15 . The method of claim 14 , wherein the Cas12a nucleic acid-guided nuclease comprises mutations to amino acid residues K579, N583 and K635 in relation to SEQ ID NO:5.
16 . The method of claim 1 , wherein the Cas12a nucleic acid-guided nuclease comprises a mutation selected from mutations to amino acid residues K613, N617 and K671 in relation to SEQ ID NO: 6.
17 . The method of claim 16 , wherein the Cas 12a nucleic acid-guided nuclease comprises at least two mutations selected from mutations to amino acid residues K613, N617 and K671 in relation to SEQ ID NO:6.
18 . The method of claim 17 , wherein the Cas12a nucleic acid-guided nuclease comprises mutations to amino acid residues K613, N617 and K671 in relation to SEQ ID NO:6.
19 . The method of claim 1 , wherein the Cas12a nucleic acid-guided nuclease comprises a mutation selected from mutations to amino acid residues K613, N617 and K671 in relation to SEQ ID NO: 7.
20 . The method of claim 19 , wherein the Cas 12a nucleic acid-guided nuclease comprises at least two mutations selected from mutations to amino acid residues K613, N617 and K671 in relation to SEQ ID NO:7.
21 . The method of claim 20 , wherein the Cas12a nucleic acid-guided nuclease comprises mutations to amino acid residues K613, N617 and K671 in relation to SEQ ID NO:7.
22 . The method of claim 1 , wherein the Cas12a nucleic acid-guided nuclease comprises a mutation selected from mutations to amino acid residues K617, N621 and K678 in relation to SEQ ID NO: 8.
23 . The method of claim 22 , wherein the Cas 12a nucleic acid-guided nuclease comprises at least two mutations selected from mutations to amino acid residues K617, N621 and K678 in relation to SEQ ID NO:8.
24 . The method of claim 23 , wherein the Cas12a nucleic acid-guided nuclease comprises mutations to amino acid residues K617, N621 and K678 in relation to SEQ ID NO:8.
25 . The method of claim 1 , further comprising the steps of:
providing a sample putatively comprising a target nucleic acid of interest; and
providing second ribonucleoprotein complexes comprising a second nucleic acid-guided nuclease that exhibits both cis- and trans-cleavage activity upon activation and a second gRNA that recognizes the target nucleic acid of interest.
26 . The method of claim 25 , wherein the target nucleic acid of interest is a DNA nucleic acid and the second nucleic acid-guided nuclease is a Cas12a or Cas14a.
27 . The method of claim 25 , wherein the target nucleic acid of interest is an RNA nucleic acid and the second nucleic acid-guided nuclease is a Cas12g or Cas13a.
28 . The method of claim 25 , further comprising the step of providing reporter moieties.
29 . The method of claim 28 , wherein the reporter moieties comprise a FRET pair.