Primary characterization of curved DNA segments cloned from Streptomyces DNA with extremely high G/C-contents.

Until recently, it was assumed that any short DNA segment could be regarded as a straight rod. Many instances, however, have been reported in which the helical axis was curved. In this study, to gain a general insight into the structural features of sequence-directed DNA curvatures, we constructed a set of plasmids carrying curved DNA segments, which were randomly cloned from Streptomyces total DNA with extremely high G/C-contents. The results of primary characterization of these curved DNA segments are presented. Although the cloned DNA segments had high G/C-contents, in all cases, several homopolymeric [dA] and [dT] stretches were found to be clustered around the centres of the determined nucleotide sequences. Furthermore, the clustered [dA] and [dT] stretches were located nearly in phase with the DNA helical screw. One of the DNA segments characterized in this study appeared to be derived from the giant linear plasmid, SCP1, and another from the circular fertility plasmid, SCP2.