PURPOSE: Plasmid pSLA3 useful as a vector in intragenic recombination by a ray fungus producing an antibiotic.

CONSTITUTION: The spore of a ray fungus Streptomyces sp. No. 7434-AN4(3) (FERM-P 6142) is inoculated into a medium and cultivated to give cleared lysates, which are separated by the centrifugation of cesium chloride-ethidium bromide to give plasmid pSLA3 having a molecular weight of 5.9W6.4 x dalton and an opened map of restricted enzyme shown by the Fig. (the numbers in the circle are molecular weight of fragment DNAs between the neighboring cut points, having megadalton unit). It has characteristics wherein a molacular weight is low, it has lot of copies, the gene dopage effect is expected, it has a box forming ability to be selected in high sensitivity, and the PstI site and sites of BamHI, XmaI, SmaI, and KpnI by partial decomposition can be applied to cloning.