A method of detecting the coincidence of two biomolecular structures in a solid phase sample, said method comprising (i) providing a first and a second fusion protein, each fusion protein comprising (a) a detection domain, said detection domain comprising a DNA binding domain; said detection domain capable of binding a cognate specific nucleotide sequence in co-operation with a further detection domain; wherein said detection domain will only bind the nucleotide sequence in co-operation when a heterotrimeric complex is formed between the nucleotide sequence, and the first and second detection domains; (b) a recognition domain, said recognition domain capable of binding a target biomolecular structure; and (c) a connector domain; said connector domain being fused at one end to the detection domain and being fused at the other end to the recognition domain; wherein at least two of (a), (b) and (c) are heterologous to one another; wherein the recognition domains of said first and said second fusion proteins are capable of binding to first and second biomolecular structures; (ii) contacting the sample with said first and second fusion proteins (iii) incubating to allow binding (iv) removing unbound fusion protein (v) contacting the sample with nucleic acid comprising said cognate specific nucleotide sequence (vi) incubating to allow heterotrimeric binding of the nucleic acid (vii) detecting nucleic acid bound to the sample wherein detection of nucleic acid in step (vii) indicates that the two biomolecular structures are present coincidentally in said sample. (i) providing a first and a second fusion protein, each fusion protein comprising (a) a detection domain, said detection domain comprising a DNA binding domain; said detection domain capable of binding a cognate specific nucleotide sequence in co-operation with a further detection domain; wherein said detection domain will only bind the nucleotide sequence in co-operation when a heterotrimeric complex is formed between the nucleotide sequence, and the first and second detection domains; (b) a recognition domain, said recognition domain capable of binding a target biomolecular structure; and (c) a connector domain; said connector domain being fused at one end to the detection domain and being fused at the other end to the recognition domain; wherein at least two of (a), (b) and (c) are heterologous to one another; wherein the recognition domains of said first and said second fusion proteins are capable of binding to first and second biomolecular structures; (a) a detection domain, said detection domain comprising a DNA binding domain; said detection domain capable of binding a cognate specific nucleotide sequence in co-operation with a further detection domain; wherein said detection domain will only bind the nucleotide sequence in co-operation when a heterotrimeric complex is formed between the nucleotide sequence, and the first and second detection domains; (b) a recognition domain, said recognition domain capable of binding a target biomolecular structure; and (c) a connector domain; said connector domain being fused at one end to the detection domain and being fused at the other end to the recognition domain; wherein at least two of (a), (b) and (c) are heterologous to one another; wherein the recognition domains of said first and said second fusion proteins are capable of binding to first and second biomolecular structures; (ii) contacting the sample with said first and second fusion proteins (iii) incubating to allow binding (iv) removing unbound fusion protein (v) contacting the sample with nucleic acid comprising said cognate specific nucleotide sequence (vi) incubating to allow heterotrimeric binding of the nucleic acid (vii) detecting nucleic acid bound to the sample wherein detection of nucleic acid in step (vii) indicates that the two biomolecular structures are present coincidentally in said sample.