RNA tagging system for visualization of single mRNA molecules

1. A single stranded nucleic acid comprising twelve to twenty four loops of 5′-ANUA-3′, wherein the 5′ end of each of the loops is directly connected to a sequence of eight nucleotides, seven nucleotides of the sequence of eight nucleotides are complementary to seven nucleotides of a sequence of seven nucleotides directly connected to the 3′ end of the same loop, such that a stem and a loop structure is formed in each of the loops, and wherein a stem of each of the loops is separated from a stem of its adjacent loop of the loops by a nucleotide sequence of 40-55 nucleotides.

2. The nucleic acid of claim 1 , wherein the nucleic acid, at its 3′ portion, further comprises two LoxP sites, optionally separated by a marker gene.

3. The nucleic acid of claim 1 , wherein the twelve to twenty four loops of 5′-ANUA-3′ are twelve loops of 5′-ANUA-3′.

4. The nucleic acid of claim 1 , wherein the nucleotide sequence of 40-55 nucleotides is a nucleotide sequence of 50 nucleotides.

5. The nucleic acid of claim 1 , wherein the stem of the stem and loop structure in each of the loops has a different sequence.

6. The nucleic acid of claim 1 , wherein the stem of the stem and loop structure in each of the loops has the same sequence.

7. A single stranded nucleic acid encoding from seven to twelve loops of 5′-ANUA-3′, wherein the 5′ end of each loop is directly connected to a sequence of eight nucleotides, seven nucleotides of the sequence of eight nucleotides are complementary to seven nucleotides of a sequence of seven nucleotides directly connected to the 3′ end of the same loop, such that a stem and loop structure is formed in each of the loops, and wherein a stem of each of the loops is separated from a stem of its adjacent loop by a nucleotide sequence of 45-55 nucleotides.

8. A kit comprising the nucleic acid of claim 1 , and instructions for use in visualizing an RNA of interest in a cell.