We have isolated and studied the cloned sigma factors SASIG1-3 from mustard (Sinapis alba). In functional ana-lyses using both promoter and factor mutants,the three recombinant proteins all had similar basic properties but also revealed differences in promoter preference and requirements for single nucleotide positions. Directedmuta-genesis of SASIG1 identified critical residues within the conserved regions and necessary for binding of the )10 and)35 promoter elements,respectively.
