RNA-antibody fusions and their selection

Details RNA-antibody fusions and their selection RNA-antibody fusions and their selection

1999-01-28

2003-02-11

Jones, W. Gary (Department: 1655)

Chemistry: molecular biology and microbiology

Measuring or testing process involving enzymes or...

Involving nucleic acid

C435S069100, C435S091210, C536S023100, C536S023400, C536S023530, C530S387100

Reexamination Certificate

active

06518018

ABSTRACT:

This invention relates to protein selection methods.
The invention was made with government support under grant F32 GM17776-01 and F32 GM17776-02. The government has certain rights in the invention.
Methods currently exist for the isolation of RNA and DNA molecules based on their functions. For example, experiments of Ellington and Szostak (Nature 346:818 (1990); and Nature 355:850 (1992)) and Tuerk and Gold (Science 249:505 (1990); and J. Mol. Biol 222:739 (1991)) have demonstrated that very rare (i.e., less than 1 in 10
13
) nucleic acid molecules with desired properties may be isolated out of complex pools of molecules by repeated rounds of selection and amplification. These methods offer advantages over traditional genetic selections in that (i) very large candidate pools may be screened (>10
15
), (ii) host viability and in vivo conditions are not concerns, and (iii) selections may be carried out even if an in vivo genetic screen does not exist. The power of in vitro selection has been demonstrated in defining novel RNA and DNA sequences with very specific protein binding functions (see, for example, Tuerk and Gold, Science 249:505 (1990); Irvine et al., J. Mol. Biol 222:739 (1991); Oliphant et al., Mol. Cell Biol. 9:2944 (1989); Blackwell et al., Science 250:1104 (1990); Pollock and Treisman, Nuc. Acids Res. 18:6197 (1990); Thiesen and Bach, Nuc. Acids Res. 18:3203 (1990); Bartel et al., Cell 57:529 (1991); Stormo and Yoshioka, Proc. Natl. Acad. Sci. USA 88:5699 (1991); and Bock et al., Nature 355:564 (1992)), small molecule binding functions (Ellington and Szostak, Nature 346:818 (1990); Ellington and Szostak, Nature 355:850 (1992)), and catalytic functions (Green et al., Nature 347:406 (1990); Robertson and Joyce, Nature 344:467 (1990); Beaudry and Joyce, Science 257:635 (1992); Bartel and Szostak, Science 261:1411 (1993); Lorsch and Szostak, Nature 371:31-36 (1994); Cuenoud and Szostak, Nature 375:611-614 (1995); Chapman and Szostak, Chemistry and Biology 2:325-333 (1995); and Lohse and Szostak, Nature 381:442-444 (1996)). A similar scheme for the selection and amplification of proteins has not been demonstrated.
SUMMARY OF THE INVENTION
The purpose of the present invention is to allow the principles of in vitro selection and in vitro evolution to be applied to proteins. The invention facilitates the isolation of proteins with desired properties from large pools of partially or completely random amino acid sequences. In addition, the invention solves the problem of recovering and amplifying the protein sequence information by covalently attaching the mRNA coding sequence to the protein molecule.
In general, the inventive method consists of an in vitro or in situ transcription/ translation protocol that generates protein covalently linked to the 3′ end of its own mRNA, i.e., an RNA-protein fusion. This is accomplished by synthesis and in vitro or in situ translation of an mRNA molecule with a peptide acceptor attached to its 3′ end. One preferred peptide acceptor is puromycin, a nucleoside analog that adds to the C-terminus of a growing peptide chain and terminates translation. In one preferred design, a DNA sequence is included between the end of the message and the peptide acceptor which is designed to cause the ribosome to pause at the end of the open reading frame, providing additional time for the peptide acceptor (for example, puromycin) to accept the nascent peptide chain before hydrolysis of the peptidyl-tRNA linkage.
If desired, the resulting RNA-protein fusion allows repeated rounds of selection and amplification because the protein sequence information may be recovered by reverse transcription and amplification (for example, by PCR amplification as well as any other amplification technique, including RNA-based amplification techniques such as 3SR or TSA). The amplified nucleic acid may then be transcribed, modified, and in vitro or in situ translated to generate mRNA-protein fusions for the next round of selection. The ability to carry out multiple rounds of selection and amplification enables the enrichment and isolation of very rare molecules, e.g., one desired molecule out of a pool of 10
15
members. This in turn allows the isolation of new or improved proteins which specifically recognize virtually any target or which catalyze desired chemical reactions.
Accordingly, in a first aspect, the invention features a method for selection of a desired protein, involving the steps of: (a) providing a population of candidate RNA molecules, each of which includes a translation initiation sequence and a start codon operably linked to a candidate protein coding sequence and each of which is operably linked to a peptide acceptor at the 3′ end of the candidate protein coding sequence; (b) in vitro or in situ translating the candidate protein coding sequences to produce a population of candidate RNA-protein fusions; and (c) selecting a desired RNA-protein fusion, thereby selecting the desired protein.
In a related aspect, the invention features a method for selection of a DNA molecule which encodes a desired protein, involving the steps of: (a) providing a population of candidate RNA molecules, each of which includes a translation initiation sequence and a start codon operably linked to a candidate protein coding sequence and each of which is operably linked to a peptide acceptor at the 3′ end of the candidate protein coding sequence; (b) in vitro or in situ translating the candidate protein coding sequences to produce a population of candidate RNA-protein fusions; (c) selecting a desired RNA-protein fusion; and (d) generating from the RNA portion of the fusion a DNA molecule which encodes the desired protein.
In another related aspect, the invention features a method for selection of a protein having an altered function relative to a reference protein, involving the steps of: (a) producing a population of candidate RNA molecules from a population of DNA templates, the candidate DNA templates each having a candidate protein coding sequence which differs from the reference protein coding sequence, the RNA molecules each comprising a translation initiation sequence and a start codon operably linked to the candidate protein coding sequence and each being operably linked to a peptide acceptor at the 3′ end; (b) in vitro or in situ translating the candidate protein coding sequences to produce a population of candidate RNA-protein fusions; and (c) selecting an RNA-protein fusion having an altered function, thereby selecting the protein having the altered function.
In yet another related aspect, the invention features a method for selection of a DNA molecule which encodes a protein having an altered function relative to a reference protein, involving the steps of: (a) producing a population of candidate RNA molecules from a population of candidate DNA templates, the candidate DNA templates each having a candidate protein coding sequence which differs from the reference protein coding sequence, the RNA molecules each comprising a translation initiation sequence and a start codon operably linked to the candidate protein coding sequence and each being operably linked to a peptide acceptor at the 3′ end; (b) in vitro or in situ translating the candidate protein coding sequences to produce a population of RNA-protein fusions; (c) selecting an RNA-protein fusion having an altered function; and (d) generating from the RNA portion of the fusion a DNA molecule which encodes the protein having the altered function.
In yet another related aspect, the invention features a method for selection of a desired RNA, involving the steps of: (a) providing a population of candidate RNA molecules, each of which includes a translation initiation sequence and a start codon operably linked to a candidate protein coding sequence and each of which is operably linked to a peptide acceptor at the 3′ end of the candidate protein coding sequence; (b) in vitro or in situ translating the candidate protein coding sequences to produce a population of candidate RNA-

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