DNA sequence of ref(2)P^p and ref(2)P^o1 have been compared, revealing numerous point mutations all along the sequence. Four main variations are (i) In exon 1, ref(2)P^o1 encodes glutamine-asparagine (nucleotides 453-458 read CAGAAT), ref(2)P^p encodes glycine (nucleotides GGA), (ii) In exon 2, ref(2)P^p has a 21bp deletion between positions 1556 and 1578, (iii) In exon 2, ref(2)P^p has a 24bp deletion between positions 2196 and 2221, (iv) In intron 1 of ref(2)P^p a 7bp insertion is a perfect repeat of a motif that may be important in secondary structure and is present 23bp upstream. Sequence of ref(2)P^o2 differs from that for ref(2)P^o1 by four point mutations. Three are in coding regions for exon 2 or 3, where a serine in ref(2)P^o1 is replaced by an arginine in ref(2)P^o2, an aspartic acid by a glutamic acid and a threonine by a serine.

Permissive (susceptible) line to the sigma virus, determined by a CO₂ sensitivity assay.