  We discuss possible mechanisms that may impact the order of the transition
between denaturated and bound DNA states and lead to changes in the scaling
laws that govern conformational properties of DNA strands. To this end, we
re-consider the Poland-Scheraga model and apply a polymer field theory approach
to calculate entropic exponents associated with the denaturated loop
distribution. We discuss in particular variants of this transition that may
occur due to the properties of the solution and may affect the self- and mutual
interaction of both single and double strands. We find that the effects studied
significantly influence the strength of the first order transition. This is
manifest in particular by the changes in the scaling laws that govern DNA loop
and strand distribution. As a quantitative measure of these changes we present
the values of corresponding scaling exponents. For the $d=4-\varepsilon$ case
we get corresponding $\varepsilon^4$ expansions and evaluate the perturbation
theory expansions at space dimension $d=3$ by means of resummation technique.
