FruB is an associated protein of FruA, a transcription factor essential for the development of Myxococcus xanthus. Degenerate oligonucleotide primers were designed based on the N-terminal amino acid sequence of FruB. Using genomic DNA as template, an approximate 110 bp fragment was generated and further served as a probe to screen a small genomic library of M. xanthus. A 4.5 kb SacI fragment was isolated on the basis of its homology to the probe. Disruption of fruB delayed the morphogenesis of fruiting bodies and depressed spore yield, suggesting that to some extent, FruB might be involved in the development of M. xanthus.