noise 1 (MN1) universality class [@MN1; @MN2; @MN3; @MN4]. On the other hand, a wall limiting negative values of the interface height (lower wall) leads to a different type of phase transition as shown by T. Hwa and one of us some years back [@MN3]. In what follows, and following the nomenclature introduced in [@Review], we will use the term MN2 to name this class.

It can be easily shown that a KPZ equation with positive non-linearity and a lower wall is completely equivalent to a KPZ with a negative non-linearity coefficient and an upper wall [@Review]: one just have to change the sign of the height variable in the KPZ-like equation to verify this.

The MN2 class is of great importance in the context of alignment of DNA and other biological sequences. It has been argued by Hwa and collaborators, that the phase transition appearing upon changing the, so called, scoring parameter in the commonly used alignment algorithm can be mapped into the MN2 critical point [@Hwa]. It is also related to some instances of non-equilibrium wetting [@Haye1]. For some other applications and physical instances within this class see [@Review] and references therein.

While the MN1 class has been 