Second-site suppressors of a cold-sensitive prohead accessory protein of bacteriophage ΦX174

This study describes the isolation of second-site suppressors which correct for the defects associated with cold-sensitive (cs) prohead accessory proteins of bacteriophage ΦX174. Five phenotypically different suppressors were isolated. Three of these suppressors confer novel temperature-sensitive (ts) phenotypes. They were unable to complement a ts mutation in gene F which encodes the major coat protein of the phage. All five suppressor mutations confer nucleotide changes in the gene F DNA sequence. These changes define four amino acid sites in the gene F protein. Three suppressor mutations placed into an otherwise wild-type background display a cold resistant phenotype in liquid culture infections when compared to a wild-type ΦX174 control.