The cloning and overexpression of a cruciform binding protein from Ustilago maydis

The structural gene HMP1 encoding a cruciform DNA binding protein from Ustilago maydis has been cloned. Gene isolation was enabled by a polymerase chain reaction procedure using primers designed from amino acid sequence obtained from the purified protein. DNA sequence determination has revealed that the gene encodes a protein containing 98 amino acids with a calculated molecular weight of 10151. Comparison of the cDNA and genomic sequences indicated the presence of a single intron in the 5' coding region of the gene. The gene was over-expressed as a translational fusion with a hexahistidine leader sequence enabling affinity purification of the protein on an immobilized metal matrix. Protein isolated after over-expression exhibited cruciform binding activity, conforming earlier purified native protein results. Sequence analysis indicated that no HMG box was present and very little homology to other known cruciform binding proteins was found. It is plausible that HMP1 represents a novel class of proteins that recognize such secondary structures.