  A simple model of a circularly closed dsDNA in a poor solvent is considered
as an example of a semi-flexible polymer with self-attraction. To find the
ground states, the conformational energy is computed as a sum of the bending
and torsional elastic components and the effective self-attraction energy. The
model includes a relative orientation or sequence dependence of the effective
attraction forces between different pieces of the polymer chain. Two series of
conformations are analysed: a multicovered circle (a toroid) and a multifold
two-headed racquet. The results are presented as a diagram of state. It is
suggested that the stability of particular conformations may be controlled by
proper adjustment of the primary structure. Application of the model to other
semi-flexible polymers is considered.
