RESUMEN
In order to study the relationship between lengths of homologous fragments and chromsomic recombination rate in Saccharopolyspora erythraea, three homologous sequences, with mutant loci and different flanking sequences, (26bp + 27bp), (500bp + 576bp) and (1908bp + 1749bp), were synthesized by chemical reaction or PCR amplification, and cloned into pWHM3 to construct homologous recombination plasmids, pWHM1113, pWHM1116 and pWHM1119. When the plasmids were transformed into protoplast of Saccharopolyspora erythraea A226 under PEG mediated, on an average 30, 69 and 170 transformants grew on each plate for the three plasmids respectively, but chromosomic integration frequency were 0, 2% and 19% among corresponding transformants. Both pWHM1116 and pWHM1119 could take double crossover recombination, and exchange the mutant loci in the chromosome. It was concluded that when the flanking sequences were equal or more than (500bp + 576bp), they could take effective single and double recombination with Saccharopolyspora erythraea chromosome.