Translation-coupling systems
Disclosed are systems and methods for coupling translation of a target gene to a detectable response gene. A version of the invention includes a translation-coupling cassette. The translation-coupling cassette includes a target gene, a response gene, a response-gene translation control element, and a secondary structure-forming sequence that reversibly forms a secondary structure masking the response-gene translation control element. Masking of the response-gene translation control element inhibits translation of the response gene. Full translation of the target gene results in unfolding of the secondary structure and consequent translation of the response gene. Translation of the target gene is determined by detecting presence of the response-gene protein product. The invention further includes RNA transcripts of the translation-coupling cassettes, vectors comprising the translation-coupling cassettes, hosts comprising the translation-coupling cassettes, methods of using the translation-coupling cassettes, and gene products produced with the translation-coupling cassettes.
1. A translation-coupling cassette comprising:
a target gene or a target-gene cloning site configured for forming the target gene;
a response gene or a response-gene cloning site configured for inserting a response gene therein;
a response-gene translation control element that, in a transcript of the translation-coupling cassette, controls translation of the response gene or a response gene inserted in the response gene cloning site; and
a secondary structure-forming sequence that, in the transcript of the translation-coupling cassette, reversibly forms a secondary structure that masks the response-gene translation control element and encompasses at least a portion of the 3′ end of the coding sequence of the target gene, wherein at least part of the secondary structure-forming sequence is translationally linked with the target-gene cloning site or the target gene.
2. The translation-coupling cassette of claim 1 wherein the target-gene cloning site or the response-gene cloning site includes a multiple cloning site.
3. The translation-coupling cassette of claim 1 wherein the target-gene cloning site or the response-gene cloning site includes a ligation-independent cloning site.
4. The translation-coupling cassette of claim 1 further comprising a protein tag-encoding sequence, wherein the protein tag-encoding sequence forms or is configured to form part of the 3′ end of the target gene coding sequence.
5. The translation-coupling cassette of claim 1 wherein the response gene is a screenable gene.
6. The translation-coupling cassette of claim 1 wherein the response gene is a selectable gene.
7. The translation-coupling cassette of claim 1 wherein the response-gene translation control element is a ribosome binding site.
8. The translation-coupling cassette of claim 7 wherein the ribosome binding site comprises a Shine-Dalgarno sequence or derivative thereof.
9. The translation-coupling cassette of claim 7 wherein the ribosome binding site comprises an AT-rich sequence.
10. The translation-coupling cassette of claim 1 further comprising a linker disposed between the response-gene translation control element and the response gene or the response-gene cloning site.
11. The translation-coupling cassette of claim 1 wherein the secondary structure formed by the secondary structure-forming sequence in the transcript includes a stem loop.
12. The translation-coupling cassette of claim 1 wherein the secondary structure-forming sequence at least partially includes the response-gene translation control element.
13. The translation-coupling cassette of claim 12 wherein the secondary structure-forming sequence further includes a stop codon, the stop codon being translationally linked with the target-gene cloning site or translationally linked in-frame with the target gene.
14. The translation-coupling cassette of claim 13 wherein the secondary structure-forming sequence at least partially includes a protein tag-encoding sequence, wherein the protein tag-encoding sequence forms or is configured to form part of the 3′ end of the target gene coding sequence.
15. The translation-coupling cassette of claim 1 wherein the secondary structure-forming sequence is selected from the group consisting of bases 18-46 of SEQ ID NO:1, bases 26-60 of SEQ ID NO:2, bases 26-60 of SEQ ID NO:3, bases 26-60 of SEQ ID NO:4, and bases 5-51 of SEQ ID NO:5.
16. The translation-coupling cassette of claim 1 wherein the translation-coupling cassette is included within a vector capable of being introduced in a host.
17. The translation-coupling cassette of claim 1 further including a host comprising the translation-coupling cassette.
18. The translation-coupling cassette claim 17 wherein the host is a prokaryote.
19. The translation-coupling cassette of claim 1 wherein the secondary structure-forming sequence consists of sequence that forms secondary structure in the transcript of the translation-coupling cassette.
20. The translation-coupling cassette of claim 1 wherein the secondary structure-forming sequence comprises a base that, in the transcript of the translation-coupling cassette, base pairs directly with at least a portion of the response-gene translation control element, wherein the base is translationally linked with the target-gene cloning site or the target gene.
21. The translation-coupling cassette of claim 1 wherein the response-gene translation control element is translationally linked with the target-gene cloning site or the target gene.