Using angle-resolved photoemission spectroscopy, we studied the electronic structures of ${\mathrm{CsFe}}_{2}{\mathrm{As}}_{2}$ and ${\mathrm{RbFe}}_{2}{\mathrm{As}}_{2}$. Contrary to other iron-based superconductors where the band structures are usually depicted in the two-Fe Brillouin zone (BZ), we found that the distribution of electronic spectral weight in ${\mathrm{CsFe}}_{2}{\mathrm{As}}_{2}$ and ${\mathrm{RbFe}}_{2}{\mathrm{As}}_{2}$ follows the one-Fe BZ, and that the emerging band structure is qualitatively consistent with theoretical band calculations of the one-Fe BZ except for some shadow band effect. Our data suggest that the interlayer separation is an important tuning factor for the physics of FeAs layers, the increase of which can reduce the coupling between Fe and As and lead to the emergence of the electronic structure in accord with the one-Fe symmetry of the Fe square lattice. Our finding puts strong constraints on the theoretical models constructed on the basis of the one-Fe BZ.