A recombinant cosmid clone was isolated from a library created from cosmid pQB79-1 and B. subtilis DNA, and a 15 kb (kilobase) BamHI fragment derived from the cloned insert was transferred to the vector pHV33. The recombinant clone, pRC12, was capable of complementing 8 auxotrophic markers in the spoIIA-tyrA region of the B. subtilis chromosome (map positions 205-210). It also complemented 8 of 9 markers in the spoIIA locus. The exception, spoIIA176, is the most distal marker from lysine. Although pRC12 failed to complement sporulation defects in spoVA or spoIVA (spoIIA+) strains, subclones of pRC12, lacking a functional spoIIA gene, did complement these mutations. pRC12 inhibited sporulation in a spo+ recE strain, possibly due to the presence of multiple functional spoIIA genes. Both the original cosmid and pRC12 were unstable in Escherichia coli and B. subtilis. Antibiotic selection of the vector resulted in extensive deletion of the insert, while selection for insert function in B. subtilis invariably led to loss of the chloramphenicol resistance vector function.