Abstract: The present invention relates to a method of screening for peptides capable of binding to a ubiquitin protein ligase (E3), successful binding being determined by detecting the amount of a test protein in the cell. The invention relates to a method for determining if a peptide binds or is capable of binding to a ubiquitin protein ligase (E3) and thereby leads to degradation of a test protein, wherein the peptide is between about 7 and 110 amino acids in length, the method comprising: providing in a eukaryotic cell a candidate peptide functionally linked to a test protein, under conditions enabling ubiquitination of proteins by an E3; and detecting the amount of test protein present in the cell; whereby, a reduced amount of the test protein determines the candidate peptide as a peptide that binds or is capable of binding to an E3 (an E3-binding peptide).

Abstract: The present invention relates to nucleic acid libraries, peptide libraries and uses thereof. The invention relates to libraries of nucleic acids that encode a plurality of peptides that represent fragments of naturally occurring proteins. In particular, the invention relates to a library of nucleic acids, each nucleic acid comprising a coding region of defined nucleic acid sequence encoding for a peptide having a length of between 25 and 110 amino acids, and having an amino acid sequence being a region of a sequence selected from the amino acid sequence of a naturally occurring protein of one or more organisms; wherein the library comprises nucleic acids that encode for a plurality of at least 10,000 different such peptides, and wherein the amino acid sequence of each of at least 50 of such peptides is a sequence region of the amino acid sequence of a different protein of a plurality of different such naturally occurring proteins.