Delimitation of cohesive ends site (cos) of Streptomyces temperate bacteriophage R4.

The cohesive ends site (cos) of actinophage R4 was delimitated by assaying the in vivo packaging activity of cosmid derivatives in Streptomyces lividans. A region of 66 bp from -30 to +36 from the center of cohesive ends was required for the basal level of packaging activity. Two additional regions outside the basal sequences from -39 to -31 and from +37 to +97 were necessary for the high level of activity, defined as the accessory sequences. Direct- or inverted-repeat sequences were found within the delimitated region, which might be involved in the recognition by the terminase of actinophage R4.