Ribosomal polynucleotides and related expression systems

1. A synthetic and isolated polynucleotide encoding a mammalian 18S rRNA that is resistant to pactamycin, wherein the pactamycin-resistance is conferred by one or more single residue substitutions in the 18S rRNA sequence, wherein the one or more single residue substitutions is at a position corresponding to G963, A964, C1065 or C1066 of mouse 18S rRNA (SEQ ID NO:23); a fragment thereof harboring said substitutions; a fully complementary sequence thereto; or a substantially identical sequence of the foregoing.

2. The polynucleotide of claim 1 , wherein the single residue substitution is at a position corresponding to position G963 of SEQ ID NO:23.

3. The polynucleotide of claim 1 , wherein the single residue substitution corresponds to a G963A substitution in SEQ ID NO:23.

4. The polynucleotide of claim 1 , wherein the polynucleotide encodes human 18S rRNA or mouse 18S rRNA.

5. The polynucleotide of claim 1 , wherein the polynucleotide comprises SEQ ID NO:23 except for a G963A substitution.

6. A mammalian 18S rRNA encoded by the polynucleotide of claim 1 .

7. An expression vector expressing the polynucleotide of claim 1 .

8. The vector of claim 7 , wherein the polynucleotide further comprises the 5′ ETS and ITS1 of the rDNA sequence.

9. The vector of claim 7 , further comprises a pol-I promoter or a cytomegalovirus (CMV) promoter.

10. The vector of claim 7 , further comprises the 3′ ETS or an SV40poly(A) signal.

11. An isolated host cell harboring the expression vector of claim 7 .

12. A kit comprising the expression vector of claim 7 .

13. A kit comprising an isolated cell containing the expression vector of claim 7 .

14. A method for preferentially translating a recombinant mRNA, the method comprising:

expressing the synthetic polynucleotide of claim 1 in a mammalian cell, wherein the synthetic polynucleotide has been altered to introduce one or more mutations that confer preferential binding of the 18S rRNA to the recombinant mRNA;

providing the recombinant mRNA to the cell; and

exposing the cell to pactamycin in an amount sufficient to reduce or eliminate protein synthesis from the cell's endogenous 40S ribosomal subunits, thereby largely restricting protein synthesis in the cell to 40S ribosomal subunits comprising the 18S rRNA expressed by the synthetic polynucleotide of claim 1 and preferentially translating the recombinant mRNA.

15. A method for identifying a mutation in 18S rRNA that alters ribosomal functions, comprising:

(a) introducing an additional mutation to the synthetic polynucleotide of claim 1 ;

(b) expressing the synthetic polynucleotide bearing the additional mutation in a host cell in the presence of pactamycin; and

(c) detecting an alteration in the ribosomes of the host cell relative to that of a control cell expressing the synthetic polynucleotide without the additional mutation; thereby identifying the additional mutation as one altering ribosomal functions.

16. The method of claim 15 , wherein the synthetic polynucleotide is present in an expression vector introduced into the host cell.

17. The method of claim 15 , wherein the single residue substitution corresponds to a G963A substitution in SEQ ID N 0 :23.

18. The method of claim 15 , wherein the synthetic polynucleotide comprises SEQ ID N 0 :23 except for a G963A substitution.

19. A method for producing ribosomes with enhanced translation efficiency in a mammalian cell, comprising:

(a) introducing an additional mutation to the synthetic polynucleotide of claim 1 ;

(b) introducing the synthetic polynucleotide bearing said additional mutation into a host mammalian cell;

(c) culturing the cell in the presence of pactamycin; and

(d) detecting enhanced translation efficiency in the cell relative to that of a control cell expressing the synthetic polynucleotide without the additional mutation; thereby producing ribosomes with enhanced translation efficiency.

20. The method of claim 19 , wherein the synthetic polynucleotide is present in an expression vector introduced into the host cell.

21. The method of claim 19 , wherein the single residue substitution corresponds to a G963A substitution in SEQ ID NO:23.

22. The method of claim 19 , wherein the synthetic polynucleotide comprises SEQ ID NO:23 except for a G963A substitution.

23. The method of claim 19 , wherein translation efficiency is determined by measuring the level of a specific polypeptide in the host cell.