DNA constructs comprise a first
exon sequence of nucleotides encoding a first
peptide or polypeptide, a second
exon sequence of nucleotides encoding a second
peptide or polypeptide and a third sequence of nucleotides between the first and second sequences encoding a
heterologous intron, for example that of
Tetrahymena thermophila nuclear pre-rRNA, between
RNA splice sites and
a site-specific recombination sequence, such as loxP, within the
intron, the exons together encoding a product
peptide or polypeptide. Such constructs are of use in
methods of production of peptides or polypeptides, transcription leading to splicing out of the
intron enabling translation of a
single chain product peptide or polypeptide. Isolated
nucleic acid constructs consisting essentially of a sequence of nucleotides encoding a self-splicing intron with
a site-specific recombination sequence within the intron, for use in creation of constructs for expression of peptides or polypeptides, are also provided.