The a-screw dislocation related luminescence (DRL) in n-GaN is investigated with polarization optical spectroscopy. An unusual difference in the polarization directions of two DRL spectral components is observed: directed parallel or inclined at an angle of about 40° to the dislocation line. As a tentative explanation, that property is proposed to be due to the theoretically predicted different orientations of chemical bonds in the cores of N and Ga partials of the dissociated a-screw dislocation.