B. Arcangioli et al., SAP1, A PROTEIN THAT BINDS TO SEQUENCES-REQUIRED FOR MATING-TYPE SWITCHING, IS ESSENTIAL FOR VIABILITY IN SCHIZOSACCHAROMYCES-POMBE, Molecular and cellular biology, 14(3), 1994, pp. 2058-2065
The pattern of mating-type switching in cell pedigrees of the fission
yeast Schizosaccharomyces pombe is dictated by the inheritance of spec
ific DNA chains at the mating-type locus (mat1). The recombination eve
nt essential for switching is initiated by a site-specific double-stra
nd break at mat1. The switch-activating protein, Sap1, binds in vitro
to a mat1 cis-acting site that was shown earlier to be essential for e
fficient mating-type switching. We isolated the sap1 gene by using oli
gonucleotides corresponding to the amino acid sequence of purified Sap
1 protein. The sequence of that gene predicted a 30-kDa protein with n
o significant homology to other canonical DNA-binding protein motifs.
To facilitate its biochemical characterization, Sap1 was expressed in
Escherichia coli. The protein expressed in bacteria displayed the same
DNA-binding specificities as the protein purified from S. pombe. Inte
restingly, analysis of a sap1 null mutation showed that the gene is es
sential for growth even in a strain in which mating-type snitching is
prohibited because of a defect in generation of the double-strand brea
k. Thus, the sap1 gene product implicated in mating-type switching is
shown to be essential for cell viability.