It is known that the CR geometries of Levi non-degen-erate hypersurfaces in $C^n$ and of the elliptic or hyperbolic CR submanifolds of codimension two in $C^4$ share many common features. In this paper, a special class of normalized coordinates is introduced for any CR manifold M which is one of the above three kinds and it is shown that the explicit expression in these coordinates of an isotropy automorphism $f{in}Aut(M)_o {subset}Aut(M),;o{in}M$, is equal to the expression of a corresponding element of the automorphism group of the homogeneous model. As an application of this property, an extension theorem for CR maps is obtained.