Construct: The majority of exon 2, intron 2 and part of exon 3 has been deleted from the HindIII-XhoI genomic fragment from the ref(2)P^p mutant. The resulting fragment encodes the first 91 amino acids of the restrictive protein, including 57 amino acids from exon 1 and 34 amino acids from the beginning of exon 2, plus a glycine at the C-terminal end.