A partial DNA library of Streptomyces ansochromogenes 7100 was constructed by using plasmid pIJ702 as vector and white mutant W19 as recipient. About 3 000 clones were obtained, two of which gave rise to the grey phenotype as wild type 7100. The plasmids were isolated from two transformants. The result indicated that the 5.2 kb and 5.8 kb DNA fragments were inserted into pIJ702. The resulting recombinant plasmids were designated as pNL-1 and pNL-2 respectively. The 1.25 kb PstI I-Apa I DNA fragment from pNL-1 was recognized as its complementarity to W19 strain. The nucleotide sequence of the 3.0 kb Pst I DNA fragment including 1.25 kb was determined and analyzed. The result indicated that this DNA fragment contains one complete open reading frame (ORF1) which encodes a protein with 295 amino acid residues, and this gene was designated as sawB. The deduced protein has 81% amino acid identities in comparison with that encoded by whiH in Streptomyces coelicolor. The function of sawB gene was studied by using strategy of gene disruption, and the resulting sawB mutant failed to form spores and produced loosely coiled aerial hyphal. The result showed that sawB is closely related to hyphal coiling and sporulation in S. ansochromogenes, and also indicated that the sawB can complement whiH mutant (C119) to restore the grey phenotype of Streptomyces coelicolor J1501(wild type).